File: chapter6-d.html

package info (click to toggle)
w3-recs 20110107-1
links: PTS, VCS
area: non-free
in suites: bullseye, buster, jessie, jessie-kfreebsd, stretch, wheezy
size: 195,972 kB
ctags: 48,964
sloc: xml: 67,284; makefile: 115; perl: 31
file content (1228 lines) | stat: -rw-r--r-- 70,581 bytes
<!DOCTYPE html
  PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
   <head>
      <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
      <title>Interactions with the Host Environment</title><style type="text/css">

.egmeta {
color:#5555AA;font-style:italic;font-family:serif;font-weight:bold;
}

table.syntax {
font-size: 75%;
background-color: #DDDDDD;
border: thin  solid;
}
table.syntax td {
border: solid thin;
}
table.syntax th {
text-align: left;
}

table.attributes td { padding-left:0.5em; padding-right:0.5em; }
table.attributes td.attname { white-space:nowrap; vertical-align:top;}
table.attributes td.attdesc { background-color:#F0F0FF; padding-left:2em; padding-right:2em}

th.uname {font-size: 50%; text-align:left;}
code           { font-family: monospace; }

div.constraint,
div.issue,
div.note,
div.notice     { margin-left: 2em; }

li p           { margin-top: 0.3em;
                 margin-bottom: 0.3em; }

div.exampleInner pre { margin-left: 1em;
                       margin-top: 0em; margin-bottom: 0em}
div.exampleOuter {border: 4px double gray;
                  margin: 0em; padding: 0em}
div.exampleInner { background-color: #d5dee3;
                   border-top-width: 4px;
                   border-top-style: double;
                   border-top-color: #d3d3d3;
                   border-bottom-width: 4px;
                   border-bottom-style: double;
                   border-bottom-color: #d3d3d3;
                   padding: 4px; margin: 0em }
div.exampleWrapper { margin: 4px }
div.exampleHeader { font-weight: bold;
                    margin: 4px}
a.mainindex {font-weight: bold;}
li.sitem {list-style-type: none;}

  .error { color: red }

  div.mathml-example {border:solid thin black;
              padding: 0.5em;
              margin: 0.5em 0 0.5em 0;
             }
  div.strict-mathml-example {border:solid thin black;
              padding: 0.5em;
              margin: 0.5em 0 0.5em 0;
             }
  div.strict-mathml-example h5 {
  margin-top: -0.3em;
  margin-bottom: -0.5em;}
  var.meta {background-color:green}
  var.transmeta {background-color:red}
  pre.mathml {padding: 0.5em;
              background-color: #FFFFDD;}
  pre.mathml-fragment {padding: 0.5em;
              background-color: #FFFFDD;}
  pre.strict-mathml {padding: 0.5em;
              background-color: #FFFFDD;}
  .minitoc { border-style: solid;
             border-color: #0050B2; 
             border-width: 1px ;
             padding: 0.3em;}
  .attention { border-style: solid; 
               border-width: 1px ; 
               color: #5D0091;
               background: #F9F5DE; 
               border-color: red;
               margin-left: 1em;
               margin-right: 1em;
               margin-top: 0.25em;
               margin-bottom: 0.25em; }

  .attribute-Name { background: #F9F5C0; }
  .method-Name { background: #C0C0F9; }
  .IDL-definition { border-style: solid; 
               border-width: 1px ; 
               color: #001000;
               background: #E0FFE0; 
               border-color: #206020;
               margin-left: 1em;
               margin-right: 1em;
               margin-top: 0.25em;
               margin-bottom: 0.25em; }
  .baseline {vertical-align: baseline}

  #eqnoc1 {width: 10%}
  #eqnoc2 {width: 80%; text-align: center; }
  #eqnoc3 {width: 10%; text-align: right; }

div.div1 {margin-bottom: 1em;}
          
.h3style {
  text-align: left;
  font-family: sans-serif;
  font-weight: normal;
  color: #0050B2; 
  font-size: 125%;
}

  h4 { text-align: left;
       font-family: sans-serif;
       font-weight: normal;
       color: #0050B2; }
  h5 { text-align: left;
       font-family: sans-serif;
       font-weight: bold;
       color: #0050B2; } 

  th {background:  #E0FFE0;}

  p, blockquote, h4 { font-family: sans-serif; }
  dt, dd, dl, ul, li { font-family: sans-serif; }
  pre, code { font-family: monospace }

  a.termref {
  text-decoration: none;
  color: black;
  }

sub.diff-link {background-color: black; color: white; font-family:
sans-serif; font-weight: bold;}

.diff-add  { background-color: #FFFF99}
.diff-del  { background-color: #FF9999; text-decoration: line-through }
.diff-chg  { background-color: #99FF99 }
.diff-off  {  }


.mathml-render {
font-family: serif;
font-size: 130%;
border: solid 4px green;
padding-left: 1em;
padding-right: 1em;
}
</style><link rel="stylesheet" type="text/css" href="../../../StyleSheets/TR/W3C-REC.css">
   </head>
   <body>
      
      <h1><a name="world-interactions" id="world-interactions"></a>6 Interactions with the Host Environment
      </h1>
      <!-- TOP NAVIGATION BAR -->
      <div class="minitoc">
         
         Overview: <a href="Overview-d.html">Mathematical Markup Language (MathML) Version 3.0</a><br>
         Previous: 5 <a href="chapter5-d.html">Mixing Markup Languages for Mathematical Expressions</a><br>
         Next: 7 <a href="chapter7-d.html">Characters, Entities and Fonts</a><br><br>6 <a href="chapter6-d.html">Interactions with the Host Environment</a><br>&nbsp;&nbsp;&nbsp;&nbsp;6.1 <a href="chapter6-d.html#world.introduction">Introduction</a><br>&nbsp;&nbsp;&nbsp;&nbsp;6.2 <a href="chapter6-d.html#world.invoking.processors">Invoking MathML Processors</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.2.1 <a href="chapter6-d.html#world.recognizing.mathml">Recognizing MathML in XML</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.2.2 <a href="chapter6-d.html#world.resource.types">Resource Types for MathML Documents</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.2.3 <a href="chapter6-d.html#encoding-names">Names of MathML Encodings</a><br>&nbsp;&nbsp;&nbsp;&nbsp;6.3 <a href="chapter6-d.html#world-int-transfers">Transferring MathML</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.3.1 <a href="chapter6-d.html#world-int-transf-flavors">Basic Transfer Flavor Names and Contents</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.3.2 <a href="chapter6-d.html#world-int-transf-recommend">Recommended Behaviors when Transferring</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.3.3 <a href="chapter6-d.html#world-int-transf-discuss">Discussion</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.3.4 <a href="chapter6-d.html#world-int-transf-exa">Examples</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.3.4.1 <a href="chapter6-d.html#id.6.3.4.1">Example 1</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.3.4.2 <a href="chapter6-d.html#id.6.3.4.2">Example 2</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.3.4.3 <a href="chapter6-d.html#id.6.3.4.3">Example 3</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.3.4.4 <a href="chapter6-d.html#id.6.3.4.4">Example 4</a><br>&nbsp;&nbsp;&nbsp;&nbsp;6.4 <a href="chapter6-d.html#world-int-combine-other">Combining MathML and Other Formats</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.4.1 <a href="chapter6-d.html#interf.xhtml">Mixing MathML and XHTML</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.4.2 <a href="chapter6-d.html#interf.html">Mixing MathML and HTML, and other non-XML contexts</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.4.3 <a href="chapter6-d.html#interf.link">Linking</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.4.4 <a href="chapter6-d.html#interf.graphics">MathML and Graphical Markup</a><br>&nbsp;&nbsp;&nbsp;&nbsp;6.5 <a href="chapter6-d.html#world-int-style">Using CSS with MathML</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.5.1 <a href="chapter6-d.html#id.6.5.1">Order of processing attributes versus style sheets</a><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.5.2 <a href="chapter6-d.html#id.6.5.2">Layout engines that lack native MathML support</a><br></div>
      <div class="div1">
         <div class="div2">
            
            <h2><a name="world.introduction" id="world.introduction"></a>6.1 Introduction
            </h2>
            <p>To be effective, MathML must work well with a wide variety of
               renderers, processors, translators and editors. This chapter raises
               some of the interface issues involved in generating and rendering
               MathML. Since MathML exists primarily to encode mathematics in Web
               documents, perhaps the most important interface issues relate to
               embedding MathML in <a href="appendixh-d.html#HTML5">[HTML5]</a>,  and
               <a href="appendixg-d.html#XHTML">[XHTML]</a>, and in any newer HTML 
               when it appears.
            </p>
            <p>There are three kinds of interface issues that arise in embedding
               MathML in other XML documents. First, MathML markup must be recognized
               as valid embedded XML
               content, and not as an error.  This issue could be seen primarily as a
               question of managing namespaces in XML <a href="appendixg-d.html#Namespaces">[Namespaces]</a>.
               However, the implementation of XML namespaces and their management has
               not been well supported by recent commercial software.  As a result,
               other mechanisms have appeared to deal with "foreign
               content" in XML document types.
            </p>
            <p>Second, in the case of HTML/XHTML, MathML rendering must be
               integrated with browser software.  Some browsers already implement
               MathML rendering natively, and one can expect more browsers will do so
               in the future.  At the same time, other browsers
               have developed infrastructure to facilitate the rendering of MathML
               and other embedded XML content by third-party software or other
               built-in technology.  Examples of this built-in technology are the
               sophisticated CSS rendering engines now available, and the powerful
               implementations of JavaScript/ECMAScript that are becoming
               common. Using these browser-specific mechanisms generally requires
               additional interface markup of some sort to activate them.  In the
               case of CSS, there is a special restricted form of MathML3
               <a href="appendixh-d.html#MathMLforCSS">[MathMLforCSS]</a> that is tailored for use with
               CSS rendering engines that support CSS 2.1 <a href="appendixh-d.html#CSS21">[CSS21]</a>.
               This restricted profile of MathML3 does not offer the full
               expressiveness of MathML3, but it provides a portable simpler form
               that can be rendered acceptably on the screen by modern CSS engines.
               
            </p>
            <p>Third, other tools for generating and processing MathML must be
               able to communicate.  A number of MathML tools have been or are
               being developed, including editors, translators, computer algebra
               systems, and other scientific software.  However, since MathML
               expressions tend to be lengthy, and prone to error when entered by
               hand, special emphasis must be made to ensure that MathML can easily
               be generated by user-friendly conversion and authoring tools, and
               that these tools work together in a dependable, platform-independent,
               and vendor-independent way.
            </p>
            <p>
               This chapter applies to both content and presentation markup, and describes
               a particular processing model for the <code>semantics</code>, <code>annotation</code>
               and <code>annotation-xml</code> elements described in
               <a href="chapter5-d.html#mixing.semantic.annotations">Section&nbsp;5.1 Annotation Framework</a>.
               
            </p>
         </div>
         <div class="div2">
            
            <h2><a name="world.invoking.processors" id="world.invoking.processors"></a>6.2 Invoking MathML Processors
            </h2>
            <div class="div3">
               
               <h3><a name="world.recognizing.mathml" id="world.recognizing.mathml"></a>6.2.1 Recognizing MathML in XML
               </h3>
               <p>Within an XML document supporting namespaces <a href="appendixg-d.html#XML">[XML]</a>,
                  <a href="appendixg-d.html#Namespaces">[Namespaces]</a>, the preferred method to recognize
                  MathML markup is by the identification of the <code>math</code> element
                  in the MathML namespace by the use of the MathML namespace 
                  URI <code>http://www.w3.org/1998/Math/MathML</code>.
               </p>
               <p>The MathML namespace URI is the recommended method to embed MathML
                  within <a href="appendixg-d.html#XHTML">[XHTML]</a> documents.  However, some user-agents may
                  require supplementary information to be available to allow them to invoke
                  specific extensions to process the MathML markup.
               </p>
               <p>Markup-language specifications that wish to embed MathML may require
                  special conditions to recognize MathML markup that are independent of
                  this recommendation.  The conditions should be similar to those expressed
                  in this recommendation, and the local names of the MathML elements should
                  remain the same as those defined in this recommendation.
               </p>
            </div>
            <div class="div3">
               
               <h3><a name="world.resource.types" id="world.resource.types"></a>6.2.2 Resource Types for MathML Documents
               </h3>
               <p>Although rendering MathML expressions often takes place in
                  a Web browser, other MathML processing functions take place more
                  naturally in other applications.  Particularly common tasks include
                  opening a MathML expression in an equation editor or computer algebra
                  system.  It is important therefore to specify the encoding names
                  by which MathML fragments should be identified.
               </p>
               <p>Outside of those environments where XML namespaces are recognized,
                  media types <a href="appendixg-d.html#RFC2045">[RFC2045]</a>, <a href="appendixg-d.html#RFC2046">[RFC2046]</a> should
                  be used if possible to ensure the invocation of a MathML processor.
                  For those environments where media types are not appropriate, such as
                  clipboard formats on some platforms, the encoding names described
                  in the next section should be used.
               </p>
            </div>
            <div class="div3">
               
               <h3><a name="encoding-names" id="encoding-names"></a>6.2.3 Names of MathML Encodings
               </h3>
               <p>MathML contains two distinct vocabularies:  one for encoding visual
                  presentation, defined in <a href="chapter3-d.html">Chapter&nbsp;3 Presentation Markup</a>, and one for encoding
                  computational structure, defined in <a href="chapter4-d.html">Chapter&nbsp;4 Content Markup</a>.  Some MathML
                  applications may import and export only one of these two vocabularies,
                  while others may produce and consume each in a different way, and still
                  others may process both without any distinction between the two.  The
                  following encoding names may be used to distinguish between content
                  and presentation MathML markup when needed.
               </p>
               <ul>
                  <li>
                     <p><em>MathML-Presentation</em>:
                        The instance contains presentation MathML markup only.
                     </p>
                     <ul>
                        <li>
                           <p>Media Type: <code>application/mathml-presentation+xml</code></p>
                        </li>
                        <li>
                           <p>Windows Clipboard Flavor: <code>MathML&nbsp;Presentation</code></p>
                        </li>
                        <li>
                           <p>Universal Type Identifier: <code>public.mathml.presentation</code></p>
                        </li>
                     </ul>
                  </li>
                  <li>
                     <p><em>MathML-Content</em>:
                        The instance contains content MathML markup only.
                     </p>
                     <ul>
                        <li>
                           <p>Media Type: <code>application/mathml-content+xml</code></p>
                        </li>
                        <li>
                           <p>Windows Clipboard Flavor: <code>MathML&nbsp;Content</code></p>
                        </li>
                        <li>
                           <p>Universal Type Identifier: <code>public.mathml.content</code></p>
                        </li>
                     </ul>
                  </li>
                  <li>
                     <p><em>MathML</em> (generic):
                        The instance may contain presentation MathML markup, content MathML markup,
                        or a mixture of the two.
                     </p>
                     <ul>
                        <li>
                           <p>File name extension: <code>.mml</code></p>
                        </li>
                        <li>
                           <p>Media Type: <code>application/mathml+xml</code></p>
                        </li>
                        <li>
                           <p>Windows Clipboard Flavor: <code>MathML</code></p>
                        </li>
                        <li>
                           <p>Universal Type Identifier: <code>public.mathml</code></p>
                        </li>
                     </ul>
                  </li>
               </ul>
               <p>See <a href="appendixb-d.html">Appendix&nbsp;B Media Types Registrations</a> for more details about each of these 
                  encoding names.
               </p>
               <p>MathML 2 specified the predefined encoding values <code>MathML</code>,
                  <code>MathML-Content</code>, and <code>MathML-Presentation</code> for the
                  <code>encoding</code> attribute on the <code>annotation-xml</code> element.
                  These values may be used as an alternative to the media type for backward
                  compatibility.  See <a href="chapter5-d.html#mixing.alternate.representations">Section&nbsp;5.1.3 Alternate representations</a> and
                  <a href="chapter5-d.html#mixing.content.equiv">Section&nbsp;5.1.4 Content equivalents</a> for details.
                  Moreover, MathML 1.0 suggested the media-type <code>text/mathml</code>,
                  which has been superseded by <a href="appendixg-d.html#RFC3023">[RFC3023]</a>.
               </p>
            </div>
         </div>
         <div class="div2">
            
            <h2><a name="world-int-transfers" id="world-int-transfers"></a>6.3 Transferring MathML
            </h2>
            <p>MathML expressions are often exchanged between applications using the
               familiar copy-and-paste or drag-and-drop paradigms and are often stored
               in files or exchanged over the HTTP protocol.  This section provides
               recommended ways to process MathML during these transfers.
            </p>
            <p>The transfers of MathML fragments described in this section occur between
               the contexts of two applications by making the MathML data available in
               several flavors, often called <em>media types</em>, <em>clipboard
                  formats</em>, or <em>data flavors</em>.  These flavors are typically
               ordered by preference by the producing application, and are typically
               examined in preference order by the consuming application.  The
               copy-and-paste paradigm allows an application to <em>place</em>
               content in a central <em>clipboard</em>, with one data stream per
               <em>clipboard format</em>; a consuming application negotiates by
               choosing to read the data of the format it prefers.  The drag-and-drop
               paradigm allows an application to <em>offer</em> content by declaring
               the available formats; a potential recipient accepts or rejects a drop
               based on the list of available formats, and the drop action allows the
               receiving application to request the delivery of the data in one of the
               indicated formats.  An HTTP GET transfer, as in <a href="appendixh-d.html#HTTP11">[HTTP11]</a>,
               allows a client to submit a list of acceptable media types; the server
               then delivers the data using the one of the indicated media types.
               An HTTP POST transfer, as in <a href="appendixh-d.html#HTTP11">[HTTP11]</a>, allows a client
               to submit data labelled with a media type that is acceptable to the
               server application.
            </p>
            <p>Current desktop platforms offer copy-and-paste and drag-and-drop
               transfers using similar architectures, but with varying naming schemes
               depending on the platform.  HTTP transfers are all based on media types.
               This section specifies what transfer types applications should provide,
               how they should be named, and how they should handle the special
               <code>semantics</code>, <code>annotation</code>, and <code>annotation-xml</code>
               elements.
            </p>
            <p>To summarize the three negotiation mechanisms, the following paragraphs
               will describe transfer <em>flavors</em>, each with a <em>name</em>
               (a character string) and <em>content</em> (a stream of binary data), 
               which are <em>offered</em>, <em>accepted</em>, and/or
               <em>exported</em>.
            </p>
            <div class="div3">
               
               <h3><a name="world-int-transf-flavors" id="world-int-transf-flavors"></a>6.3.1 Basic Transfer Flavor Names and Contents
               </h3>
               <p>The names listed in <a href="chapter6-d.html#encoding-names">Section&nbsp;6.2.3 Names of MathML Encodings</a> are the exact
                  strings that should be used to identify the transfer flavors that
                  correspond to the MathML encodings.  On operating systems that allow
                  such, an application should register their support for these flavor
                  names (e.g. on Windows, a call to RegisterClipboardFormat, or, on the
                  Macintosh platform, declaration of support for the universal type
                  identifier in the application descriptor).
               </p>
               <p>When transferring MathML, an application MUST ensure the content
                  of the data transfer is a 
                  <a href="http://www.w3.org/TR/2004/REC-xml-20040204/#dt-wellformed">well-formed</a>
                  XML instance of a MathML document type.  Specifically:
                  
                  
               </p>
               <ol type="1">
                  <li>
                     <p>The instance MAY begin with an XML declaration,
                        e.g. &lt;?xml version="1.0"&gt;
                     </p>
                  </li>
                  <li>
                     <p>The instance MUST contain exactly one root <code>math</code> element.
                     </p>
                  </li>
                  <li>
                     <p>The instance MUST declare the MathML namespace
                        on the root <code>math</code> element.
                     </p>
                  </li>
                  <li>
                     <p>The instance MAY use a <code>schemaLocation</code> attribute
                        on the <code>math</code> element to indicate the location of the MathML
                        schema that describes the MathML document type to which the instance
                        conforms.  The presence of the <code>schemaLocation</code> attribute
                        does not require a consumer of the MathML instance to obtain or use
                        the referenced schema.
                     </p>
                  </li>
                  <li>
                     <p>The instance SHOULD use numeric character references
                        (e.g. &amp;#x03b1;) rather than character entity names
                        (e.g. &amp;alpha;) for greater interoperability.
                     </p>
                  </li>
                  <li>
                     <p>The instance MUST specify the character encoding, if it uses an
                        encoding other than UTF-8, either in the XML declaration, or by the use
                        of a byte-order mark (BOM) for UTF-16-encoded data.
                     </p>
                  </li>
               </ol>
            </div>
            <div class="div3">
               
               <h3><a name="world-int-transf-recommend" id="world-int-transf-recommend"></a>6.3.2 Recommended Behaviors when Transferring
               </h3>
               <p>An application that transfers MathML markup SHOULD adhere to the following
                  conventions:
               </p>
               <ol type="1">
                  <li>
                     <p>An application that supports pure presentation markup and/or pure
                        content markup SHOULD offer as many of these flavors as it has available.
                        
                     </p>
                  </li>
                  <li>
                     <p>An application that only exports one MathML flavor SHOULD name it
                        <code>MathML</code> if it is unable to determine a more specific flavor.
                        
                     </p>
                  </li>
                  <li>
                     <p>
                        If an application is able to determine a more specific flavor, it SHOULD
                        offer both the generic and specific transfer flavors, but it SHOULD only
                        deliver the specific flavor if it knows that the recipient supports it.
                        For an HTTP GET transfer, for example, the specific transfer types for
                        content and presentation markup should only be returned if they are
                        included in the the HTTP <code>Accept</code> header sent by the client.
                        
                     </p>
                  </li>
                  <li>
                     <p>
                        An application that exports the two specific transfer flavors SHOULD
                        export both the content and presentation transfer flavors, as well as
                        the generic flavor, which SHOULD combine the other two flavors using
                        a top-level MathML <code>semantics</code> element
                        (see <a href="chapter5-d.html#mixing.top.level">Section&nbsp;5.4.1 Top-level Parallel Markup</a>).
                     </p>
                  </li>
                  <li>
                     <p>
                        When an application exports a MathML fragment whose only child of the
                        root element is a <code>semantics</code> element, it SHOULD offer, after
                        the above flavors, a transfer flavor for each <code>annotation</code> or
                        <code>annotation-xml</code> element, provided the transfer flavor can be
                        recognized and named based on the <code>encoding</code> attribute value,
                        and provided the annotation key is (the default)
                        <a href="http://www.openmath.org/cd/mathmlkeys.xhtml#alternate-representation">alternate-representation</a>.
                        The transfer content for each annotation should contain the character data
                        in the specified encoding (for an <code>annotation</code> element), or a
                        well-formed XML fragment (for an <code>annotation-xml</code> element), or
                        the data that results by requesting the URL given by the <code>src</code>
                        attribute (for an annotation reference).
                     </p>
                  </li>
                  <li>
                     <p>As a final fallback, an application MAY export a version of
                        the data in a plain-text flavor (such as <code>text/plain</code>,
                        <code>CF_UNICODETEXT</code>, <code>UnicodeText</code>, or
                        <code>NSStringPboardType</code>).  When an application has multiple
                        versions of an expression available, it may choose the version to
                        export as text at its discretion.  Since some older MathML processors
                        expect MathML instances transferred as plain text to begin with a
                        <code>math</code> element, the text version SHOULD generally omit the XML 
                        declaration, DOCTYPE declaration, and other XML prolog material that
                        would appear before the <code>math</code> element.  The Unicode
                        text version of the data SHOULD always be the last flavor exported,
                        following the principle that exported flavors should be ordered with
                        the most specific flavor first and the least specific flavor last.
                        
                     </p>
                  </li>
               </ol>
            </div>
            <div class="div3">
               
               <h3><a name="world-int-transf-discuss" id="world-int-transf-discuss"></a>6.3.3 Discussion
               </h3>
               <p>To determine whether a MathML instance is pure content markup or
                  pure presentation markup, the <code>math</code>, <code>semantics</code>,
                  <code>annotation</code> and <code>annotation-xml</code> elements should be
                  regarded as belonging to both the presentation and content markup
                  vocabularies.  The <code>math</code> element is treated in this way
                  because it is required as the root element in any MathML transfer.
                  The <code>semantics</code> element and its child annotation elements
                  comprise an arbitrary annotation mechanism within MathML, and are
                  not tied to either presentation or content markup.  Consequently,
                  an application that consumes MathML should always process these four
                  elements, even if it only implements one of the two vocabularies.
               </p>
               <p>It is worth noting that the above recommendations allow agents
                  that produce MathML to provide binary data for the clipboard, for
                  example in an image or other application-specific format.  The sole
                  method to do so is to reference the binary data using the <code>src</code>
                  attribute of an annotation, since XML character data does not allow
                  for the transfer of arbitrary byte-stream data.
               </p>
               <p>While the above recommendations are intended to improve
                  interoperability between MathML-aware applications that use these
                  transfer paradigms, it should be noted that they do not guarantee
                  interoperability.  For example, references to external resources
                  (e.g. stylesheets, etc.) in MathML data can cause interoperability
                  problems if the consumer of the data is unable to locate them,
                  as can happen when cutting and pasting HTML or other data types.
                  An application that makes use of references to external resources
                  is encouraged to make users aware of potential problems and provide
                  alternate ways to obtain the referenced resources.  In general,
                  consumers of MathML data that contains references they cannot
                  resolve or do not understand should ignore the external references.
                  
               </p>
            </div>
            <div class="div3">
               
               <h3><a name="world-int-transf-exa" id="world-int-transf-exa"></a>6.3.4 Examples
               </h3>
               <div class="div4">
                  
                  <h4><a name="id.6.3.4.1" id="id.6.3.4.1"></a>6.3.4.1 Example 1
                  </h4>
                  <p>An e-Learning application has a database of quiz questions, some of
                     which contain MathML.  The MathML comes from multiple sources, and the
                     e-Learning application merely passes the data on for display, but does
                     not have sophisticated MathML analysis capabilities.  Consequently,
                     the application is not aware whether a given MathML instance is pure
                     presentation or pure content markup, nor does it know whether the
                     instance is valid with respect to a particular version of the MathML schema.  It therefore
                     places the following data formats on the clipboard:
                  </p>
                  <table id="table-flavor-a" border="1">
                     <thead>
                        <tr>
                           <th>Flavor Name</th>
                           <th>Flavor Content</th>
                        </tr>
                     </thead>
                     <tbody>
                        <tr>
                           <td><code>MathML</code></td>
                           <td><pre class="mathml-fragment">&lt;?xml version="1.0"?&gt;
&lt;math xmlns="http://www.w3.org/1998/Math/MathML"&gt;...&lt;/math&gt;</pre></td>
                        </tr>
                        <tr>
                           <td><code>Unicode&nbsp;Text</code></td>
                           <td><pre class="mathml-fragment">&lt;math xmlns="http://www.w3.org/1998/Math/MathML"&gt;...&lt;/math&gt;</pre></td>
                        </tr>
                     </tbody>
                  </table>
               </div>
               <div class="div4">
                  
                  <h4><a name="id.6.3.4.2" id="id.6.3.4.2"></a>6.3.4.2 Example 2
                  </h4>
                  <p>An equation editor on the Windows platform is able to generate pure presentation markup,
                     valid with respect to MathML 3.  Consequently, it
                     exports the following flavors:
                  </p>
                  <table id="table-flavor-b" border="1">
                     <thead>
                        <tr>
                           <th>Flavor Name</th>
                           <th>Flavor Content</th>
                        </tr>
                     </thead>
                     <tbody>
                        <tr>
                           <td><code>MathML&nbsp;Presentation</code></td>
                           <td><pre class="mathml-fragment">&lt;?xml version="1.0"?&gt;
&lt;math xmlns="http://www.w3.org/1998/Math/MathML"&gt;...&lt;/math&gt;</pre></td>
                        </tr>
                        <tr>
                           <td><code>Tiff</code></td>
                           <td>(a rendering sample)</td>
                        </tr>
                        <tr>
                           <td><code>Unicode&nbsp;Text</code></td>
                           <td><pre class="mathml-fragment">&lt;math xmlns="http://www.w3.org/1998/Math/MathML"&gt;...&lt;/math&gt;</pre></td>
                        </tr>
                     </tbody>
                  </table>
               </div>
               <div class="div4">
                  
                  <h4><a name="id.6.3.4.3" id="id.6.3.4.3"></a>6.3.4.3 Example 3
                  </h4>
                  <p>A schema-based content management system on the Mac OS X platform contains multiple MathML 
                     representations of a collection of mathematical expressions, including mixed 
                     markup from authors, pure content markup for interfacing to symbolic computation 
                     engines, and pure presentation markup for print publication. Due to the system's 
                     use of schemata, markup is stored with a namespace prefix. 
                     The system therefore can transfer the following data:
                  </p>
                  <table id="table-flavor-c" border="1">
                     <thead>
                        <tr>
                           <th>Flavor Name</th>
                           <th>Flavor Content</th>
                        </tr>
                     </thead>
                     <tbody>
                        <tr>
                           <td><code>public.mathml.presentation</code></td>
                           <td><pre class="mathml-fragment">&lt;?xml version="1.0"?&gt;
&lt;mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation=
             "http://www.w3.org/Math/XMLSchema/mathml3/mathml3.xsd"&gt;
  &lt;mml:mrow&gt;
  ...
  &lt;mml:mrow&gt;
&lt;/mml:math&gt;</pre></td>
                        </tr>
                        <tr>
                           <td><code>public.mathml.content</code></td>
                           <td><pre class="mathml-fragment">&lt;?xml version="1.0"?&gt;
&lt;mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation=
             "http://www.w3.org/Math/XMLSchema/mathml3/mathml3.xsd"&gt;
  &lt;mml:apply&gt;
  ...
  &lt;mml:apply&gt;
&lt;/mml:math&gt;</pre></td>
                        </tr>
                        <tr>
                           <td><code>public.mathml</code></td>
                           <td><pre class="mathml-fragment">&lt;?xml version="1.0"?&gt;
&lt;mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation=
             "http://www.w3.org/Math/XMLSchema/mathml3/mathml3.xsd"&gt;
  &lt;mml:mrow&gt;
    &lt;mml:apply&gt;
       ... content markup within presentation markup ...
    &lt;/mml:apply&gt;
    ...
  &lt;/mml:mrow&gt;
&lt;/mml:math&gt; </pre></td>
                        </tr>
                        <tr>
                           <td><code>public.plain-text.tex</code></td>
                           <td><pre class="TeX">{x \over x-1}</pre></td>
                        </tr>
                        <tr>
                           <td><code>public.plain-text</code></td>
                           <td><pre class="mathml-fragment">&lt;mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation=
             "http://www.w3.org/Math/XMLSchema/mathml3/mathml3.xsd"&gt;
  &lt;mml:mrow&gt;
  ...
  &lt;mml:mrow&gt;
&lt;/mml:math&gt;</pre></td>
                        </tr>
                     </tbody>
                  </table>
               </div>
               <div class="div4">
                  
                  <h4><a name="id.6.3.4.4" id="id.6.3.4.4"></a>6.3.4.4 Example 4
                  </h4>
                  <p>A similar content management system is web-based and delivers MathML
                     representations of mathematical expressions. The system is able to produce
                     MathML-Presentation, MathML-Content, TeX and pictures in TIFF format.
                     In web-pages being browsed, it could produce a MathML fragment such as the following:
                     
                     
                  </p><pre class="mathml-fragment">&lt;mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"&gt;
  &lt;mml:semantics&gt;
    &lt;mml:mrow&gt;...&lt;/mml:mrow&gt;
    &lt;mml:annotation-xml encoding="MathML-Content"&gt;...&lt;/mml:annotation-xml&gt;
    &lt;mml:annotation encoding="TeX"&gt;{1 \over x}&lt;/mml:annotation&gt;
    &lt;mml:annotation encoding="image/tiff" src="formula3848.tiff"/&gt;
  &lt;/mml:semantics&gt;
&lt;/mml:math&gt;
</pre><p>A web-browser on the Windows platform that receives such a fragment and tries to export it as part of
                     a drag-and-drop action, can offer the following flavors:
                  </p>
                  <table id="table-flavor-d" border="1">
                     <thead>
                        <tr>
                           <th>Flavor Name</th>
                           <th>Flavor Content</th>
                        </tr>
                     </thead>
                     <tbody>
                        <tr>
                           <td><code>MathML&nbsp;Presentation</code></td>
                           <td><pre class="mathml-fragment">&lt;?xml version="1.0"?&gt;
&lt;mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation=
             "http://www.w3.org/Math/XMLSchema/mathml3/mathml3.xsd"&gt;
  &lt;mml:mrow&gt;
  ...
  &lt;mml:mrow&gt;
&lt;/mml:math&gt;</pre></td>
                        </tr>
                        <tr>
                           <td><code>MathML&nbsp;Content</code></td>
                           <td><pre class="mathml-fragment">&lt;?xml version="1.0"?&gt;
&lt;mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation=
             "http://www.w3.org/Math/XMLSchema/mathml3/mathml3.xsd"&gt;
  &lt;mml:apply&gt;
  ...
  &lt;mml:apply&gt;
&lt;/mml:math&gt;</pre></td>
                        </tr>
                        <tr>
                           <td><code>MathML</code></td>
                           <td><pre class="mathml-fragment">&lt;?xml version="1.0"?&gt;
&lt;mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation=
             "http://www.w3.org/Math/XMLSchema/mathml3/mathml3.xsd"&gt;
  &lt;mml:mrow&gt;
    &lt;mml:apply&gt;
       ... content markup within presentation markup ...
    &lt;/mml:apply&gt;
    ...
  &lt;/mml:mrow&gt;
&lt;/mml:math&gt; </pre></td>
                        </tr>
                        <tr>
                           <td><code>TeX</code></td>
                           <td><pre class="TeX">{x \over x-1}</pre></td>
                        </tr>
                        <tr>
                           <td><code>CF_TIFF</code></td>
                           <td>(the content of the picture file, requested from formula3848.tiff)</td>
                        </tr>
                        <tr>
                           <td><code>CF_UNICODETEXT</code></td>
                           <td><pre class="mathml-fragment">&lt;mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation=
             "http://www.w3.org/Math/XMLSchema/mathml3/mathml3.xsd"&gt;
  &lt;mml:mrow&gt;
  ...
  &lt;mml:mrow&gt;
&lt;/mml:math&gt;</pre></td>
                        </tr>
                     </tbody>
                  </table>
               </div>
            </div>
         </div>
         <div class="div2">
            
            <h2><a name="world-int-combine-other" id="world-int-combine-other"></a>6.4 Combining MathML and Other Formats
            </h2>
            <p>MathML is usually used in combination with other markup languages.
               The most typical case is perhaps the use of MathML within a
               document-level markup language, such as XHTML or DocBook.  It is also
               common that other object-level markup languages are also included in a
               compound document format, such as the W3C XHTML+MathML+SVG
               profile. Other common use cases include mixing other markup within
               MathML.  For example, an authoring tool might insert an element
               representing a cursor position or other state information within
               MathML markup, so that an author can pick up editing where he or
               she left off.
            </p>
            <p>Most document markup languages have some concept of an inline
               equation, (or graphic, object, etc.) so there is a typically a natural
               way to incorporate MathML instances into the content
               model.  However, in the other direction, embedding of markup within
               MathML is not so clear cut, since in many MathML elements, the role of
               child elements is defined by position.  For example, the first
               child of an <code>apply</code> must be an operator, and the second child
               of an <code>mfrac</code> is the denominator.  The proper behavior when
               foreign markup appears in such contexts is problematic. Even when such
               behavior can be defined in a particular context, it presents an
               implementation challenge for generic MathML processors.
            </p>
            <p>For this reason, the default MathML schema does not allow
               foreign markup elements to be included within MathML
               instances.
            </p>
            <p>In the standard schema, elements from other namespaces
               are not allowed, but attributes from other namespaces are permitted.
               MathML processors that encounter unknown XML markup should behave
               as follows:
               
            </p>
            <ol type="1">
               <li>
                  <p>An attribute from a non-MathML namespace should be silently ignored.</p>
               </li>
               <li>
                  <p>An element from a non-MathML namespace should be treated
                     as an error, except in an <code>annotation-xml</code> element.
                     If the element is a child of a presentation element, it should be
                     handled as described in <a href="chapter3-d.html#presm.merror">Section&nbsp;3.3.5 Error Message <code>&lt;merror&gt;</code></a>.
                     If the element is a child of a content element, it should be
                     handled as described in <a href="chapter4-d.html#contm.cerror">Section&nbsp;4.2.9 Error Markup <code>&lt;cerror&gt;</code></a>.
                  </p>
               </li>
            </ol>
            <p>
               
               For example, if the second child of an <code>mfrac</code> element is an
               unknown element, the fraction should be rendered with a denominator
               that indicates the error.
               
            </p>
            <p>When designing a compound document format in which MathML is included in a larger document type, the designer may extend the
               content model of MathML to allow additional elements. For example, a common extension is to extend the MathML schema such
               that elements from non-MathML namespaces are
               allowed in token elements, but not in other elements. MathML processors that
               encounter unknown markup should behave as follows:
               
            </p>
            <ol type="1">
               <li>
                  <p>An unrecognized XML attribute should be silently ignored.</p>
               </li>
               <li>
                  <p>An unrecognized element in a MathML token element should be silently ignored.</p>
               </li>
               <li>
                  <p>An element from a non-MathML namespace should be treated
                     as an error, except in an <code>annotation-xml</code> element.
                     If the element is a child of a presentation element, it should be
                     handled as described in <a href="chapter3-d.html#presm.merror">Section&nbsp;3.3.5 Error Message <code>&lt;merror&gt;</code></a>.
                     If the element is a child of a content element, it should be
                     handled as described in <a href="chapter4-d.html#contm.cerror">Section&nbsp;4.2.9 Error Markup <code>&lt;cerror&gt;</code></a>.
                  </p>
               </li>
            </ol>
            <p>Extending the schema in this way is easily achieved using the Relax NG schema described in <a href="appendixa-d.html">Appendix&nbsp;A Parsing MathML</a>, it may be as simple as including the MathML schema whilst overriding the content model of <code>mtext</code>:
               
            </p><pre>

default namespace m = "http://www.w3.org/1998/Math/MathML"

include "mathml3.rnc" {
mtext = element mtext {mtext.attributes, (token.content|anyElement)*}
}
</pre><p>
               The definition given here would allow any well formed XML that is not in the MathML namespace as a child of <code>mtext</code>. In practice this may be too lax. For example, an XHTML+MathML Schema may just want to allow inline XHTML elements as additional
               children of <code>mtext</code>. This may be achieved by replacing <code>anyElement</code> by a suitable production from the <span class="diff-chg">schema</span> for the host document type.
            </p>
            <p>Considerations about mixing markup vocabularies in compound
               documents arise when a compound document type is first designed.
               But once the document type is fixed, it is not generally practical
               for specific software tools to further modify the content model to
               suit their needs.
               However, it is still frequently the case that such tools may need to
               persist additional information within a MathML instance.  Since MathML
               is most often generated by authoring tools, a particularly common and
               important case is where an authoring tool needs to persist information
               about its internal state along with a MathML expression, so an author
               can resume editing from a previous state.  For example, placeholders
               may be used to indicate incomplete parts of an expression, or a
               insertion point within an expression may need to be persisted.
            </p>
            <p>An application that needs to persist private data within a MathML
               expression should generally attempt to do so without altering the
               underlying content model, even in situations where it is feasible to
               do so.  To support this requirement, regardless of what may be allowed
               by the content model of a particular compound document format, MathML
               permits the persistence of private data via the following strategies:
            </p>
            <ol type="1">
               <li>
                  <p>For small amounts of data, attributes from other namespaces
                     are allowed on all MathML elements.
                  </p>
               </li>
               <li>
                  <p>For larger amounts of data, applications may use the 
                     <code>semantics</code> element, as described in
                     <a href="chapter5-d.html#mixing.semantic.annotations">Section&nbsp;5.1 Annotation Framework</a>.
                  </p>
               </li>
               <li>
                  <p>For authoring tools and other applications that need to
                     associate particular actions with presentation MathML subtrees,
                     e.g. to mark an incomplete expression to be filled in by an author,
                     the <code>maction</code> element may be used, as described in
                     <a href="chapter3-d.html#presm.maction">Section&nbsp;3.7.1 Bind Action to Sub-Expression
                        <code>&lt;maction&gt;</code></a>.
                  </p>
               </li>
            </ol>
            <div class="div3">
               
               <h3><a name="interf.xhtml" id="interf.xhtml"></a>6.4.1 Mixing MathML and XHTML
               </h3>
               <p>To fully integrate MathML into XHTML, it should be possible not
                  only to embed MathML in XHTML (as described in <a href="chapter6-d.html#world.recognizing.mathml">Section&nbsp;6.2.1 Recognizing MathML in XML</a>, but also see <a href="chapter2-d.html#interf.toplevel">Section&nbsp;2.2 The Top-Level 
                     <code>math</code> Element</a>), but also to embed XHTML in MathML.  However,
                  fragments using MathML extended in this way can not be reliably used
                  in other MathML systems that do not support the compound document
                  format.  Therefore, at present, the MathML specification does not
                  allow XHTML elements within a MathML expression, although when
                  specifying a particular instance of a compound document format using
                  both XHTML and MathML, the designer may wish to extend the MathML
                  Schema to allow certain XHTML elements as children of MathML token
                  elements; <code>mtext</code> may be the most suitable element for such an
                  extension as described above.
               </p>
               <p>In most cases, XHTML elements (headings, paragraphs, lists, etc.)
                  either do not apply in mathematical contexts, or MathML already
                  provides equivalent or improved functionality specifically tailored
                  to mathematical content (tables, mathematics style changes,
                  etc.).
               </p>
               <p>While the use of namespaces to embed MathML in other XML
                  applications is completely described by <a href="appendixg-d.html#Namespaces">[Namespaces]</a>,
                  a certain degree of pragmatism is necessary.
                  Support for XML, namespaces, and rendering behaviors in
                  popular user agents is not currently in alignment with W3C
                  Recommendations.  When using namespace prefixes with MathML
                  markup, some situations require the of use <code>m:</code>
                  as a conventional namespace prefix for MathML markup.  Using
                  this conventional namespace prefix may provide better
                  compatibility in current user agents.  For example:
                  
               </p><pre>
&lt;body&gt;
...
&lt;m:math xmlns:m="http://www.w3.org/1998/Math/MathML"&gt;
&lt;m:mrow&gt;...&lt;m:mrow&gt;
&lt;/m:math&gt;
...
&lt;/body&gt;
</pre><p>Consult the <a href="http://www.w3.org/Math/">W3C Math Working
                     Group</a> home page for compatibility and implementation suggestions
                  for current browsers and other MathML-aware tools.
               </p>
            </div>
            <div class="div3">
               
               <h3><a name="interf.html" id="interf.html"></a>6.4.2 Mixing MathML and HTML, and other non-XML contexts
               </h3>
               <p>MathML is defined as an XML vocabulary and may be included into many
                  larger XML document types of which XHTML is an important example as
                  discussed in the previous section. There may be other non-XML
                  vocabularies which require markup for Mathematical expressions, where it
                  makes sense to reference this specification. If a non-XML syntax is used
                  for MathML then formally this specification
                  does not apply. However implementations of such a syntax should, if possible, 
                  offer a facility to output any mathematical expressions as MathML in the XML syntax
                  defined here. Such an application would then be a
                  MathML-output-conformant processor as described in
                  <a href="chapter2-d.html#fund.mathmlconf">Section&nbsp;2.3.1 MathML Conformance</a>.
               </p>
               <p>An important example of such a non-XML based system is defined in <a href="appendixh-d.html#HTML5">[HTML5]</a>.  HTML5 incorporates MathML using a slightly
                  modified syntax
                  (for example, in HTML5, some attribute values need not be surrounded by quotes)
                  in documents served with media type text/html. <a href="appendixh-d.html#HTML5">[HTML5]</a> contains details for how
                  MathML is included in HTML5 (and XHTML5).
               </p>
            </div>
            <div class="div3">
               
               <h3><a name="interf.link" id="interf.link"></a>6.4.3 Linking
               </h3>
               <p>In MathML 3, an element is designated as a link by the presence of
                  the <code>href</code> attribute.  MathML has no element that corresponds
                  to the HTML/XHTML anchor element <var>a</var>. 
               </p>
               <p>MathML allows the <code>href</code> attribute on all
                  elements. 
                  However, most user agents have no way
                  to implement nested links or links on elements with no visible rendering;
                  such links may have no effect.
                  
               </p>
               <p>The list of presentation markup elements that do not ordinarily
                  have a visual rendering, and thus should not be used as linking
                  elements, is given in the table below.
                  
                  
               </p>
               <table id="table-nolink" width="75%">
                  <thead>
                     <tr>
                        <th colspan="2">MathML elements that should not be linking elements</th>
                     </tr>
                  </thead>
                  <tbody>
                     <tr>
                        <td><code>mprescripts</code></td>
                        <td><code>none</code></td>
                     </tr>
                     <tr>
                        <td><code>malignmark</code></td>
                        <td><code>maligngroup</code></td>
                     </tr>
                  </tbody>
               </table>
               <p>For compound document formats that support linking mechanisms, the
                  <code>id</code> attribute should
                  be used to specify the location for a link into a MathML expression.  The
                  <code>id</code> attribute is allowed on all MathML elements, and its value
                  must be unique within a document, making it ideal for this purpose.
               </p>
               <p>Note that MathML 2 has no direct support for linking; it refers to
                  the W3C Recommendation "XML Linking Language" <a href="appendixh-d.html#XLink">[XLink]</a> in
                  defining links in compound document contexts by using an <code>xlink:href</code> attribute.
                  As mentioned above, MathML 3 adds an <code>href</code>
                  attribute for linking so that <code>xlink:href</code> is no longer needed.
                  However, <code>xlink:href</code> is still allowed because MathML permits the use of attributes
                  from non-MathML namespaces. It is recommended that new compound document
                  formats use the MathML 3 <code>href</code> attribute for linking. When user agents
                  encounter MathML elements with both <code>href</code> and <code>xlink:href</code> attributes, the
                  <code>href</code> attribute should take precedence. To support backward
                  compatibility, user agents that implement XML Linking
                  in compound documents containing MathML 2 should continue to support
                  the use of the <code>xlink:href</code> attribute in addition to supporting the <code>href</code> attribute.
                  
               </p>
            </div>
            <div class="div3">
               
               <h3><a name="interf.graphics" id="interf.graphics"></a>6.4.4 MathML and Graphical Markup
               </h3>
               <p>Apart from the introduction of new glyphs, many of the situations
                  where one might be inclined to use an image amount to displaying
                  labeled diagrams. For example, knot diagrams, Venn diagrams, Dynkin
                  diagrams, Feynman diagrams and commutative diagrams all fall into this
                  category. As such, their content would be better encoded via some
                  combination of structured graphics and MathML markup.  However, at the
                  time of this writing, it is beyond the scope of the W3C Math Activity
                  to define a markup language to encode such a general concept as
                  "labeled diagrams." (See <a href="http://www.w3.org/Math/">http://www.w3.org/Math</a> for
                  current W3C activity in mathematics and <a href="http://www.w3.org/Graphics/">http://www.w3.org/Graphics</a>
                  for the W3C graphics activity.)
               </p>
               <p>One mechanism for embedding additional graphical content is via the
                  <code>semantics</code> element, as in the following example:
                  
               </p><pre>&lt;semantics&gt;
  &lt;apply&gt;
    &lt;intersect/&gt;
    &lt;ci&gt;A&lt;/ci&gt;
    &lt;ci&gt;B&lt;/ci&gt;
  &lt;/apply&gt;
  &lt;annotation-xml encoding="image/svg+xml"&gt;
    &lt;svg xmlns="http://www.w3.org/2000/svg"  viewBox="0 0 290 180"&gt;
      &lt;clipPath id="a"&gt;
      &lt;circle cy="90" cx="100" r="60"/&gt;
      &lt;/clipPath&gt;
      &lt;circle fill="#AAAAAA" cy="90" cx="190"
              r="60" style="clip-path:url(#a)"/&gt;
      &lt;circle stroke="black" fill="none" cy="90" cx="100" r="60"/&gt;
      &lt;circle stroke="black" fill="none" cy="90" cx="190" r="60"/&gt;
    &lt;/svg&gt;
  &lt;/annotation-xml&gt;
  &lt;annotation-xml encoding="application/xhtml+xml"&gt;
    &lt;img xmlns="http://www.w3.org/1999/xhtml"
         src="intersect.gif" alt="A intersect B"/&gt;
  &lt;/annotation-xml&gt;
&lt;/semantics&gt;</pre><p>
                  Here, the <code>annotation-xml</code> elements are used to indicate alternative
                  representations of the MathML-Content depiction of the
                  intersection of two sets.
                  The first one is in the "Scalable Vector
                  Graphics" format <a href="appendixh-d.html#SVG1.1">[SVG1.1]</a>
                  (see <a href="appendixh-d.html#XHTML-MathML-SVG">[XHTML-MathML-SVG]</a> for the definition of an XHTML profile integrating MathML and SVG), the second one uses the
                  XHTML <code>img</code> element embedded as an XHTML fragment.
                  In this situation, a MathML processor can use any of these
                  representations for display,  perhaps producing a graphical format
                  such as the image below.
               </p>
               <blockquote>
                  <p><img src="image/intersect.gif" alt="\includegraphics{intersect}"></p>
               </blockquote>
               <p>Note that the semantics representation of this example is given
                  in  MathML-Content markup, as the first child of the
                  <code>semantics</code> element.  In this regard, it is the
                  representation most analogous to the <code>alt</code> attribute of the
                  <code>img</code> element in XHTML, and would likely be
                  the best choice for non-visual rendering.
               </p>
            </div>
         </div>
         <div class="div2">
            
            <h2><a name="world-int-style" id="world-int-style"></a>6.5 Using CSS with MathML
            </h2>
            <p>When MathML is rendered in an environment that supports CSS <a href="appendixh-d.html#CSS21">[CSS21]</a>,
               controlling mathematics style properties with a CSS style sheet is desirable,
               but not as simple as it might first appear, because the formatting of MathML layout schemata
               is quite different from the CSS visual formatting model and many of the style parameters that affect
               mathematics layout have no direct textual analogs.
               Even in cases where there are analogous properties, the sensible values for
               these properties may not correspond. 
               Because of this difference, applications that support MathML natively may choose to 
               restrict the CSS properties applicable to MathML layout schemata to those 
               properties that do not affect layout.
               
            </p>
            <p>Generally speaking, the model for CSS interaction with the math
               style attributes runs as follows.  A CSS style sheet might provide a style
               rule such as:
            </p><pre>
math *.[mathsize="small"] {
  font-size: 80%
}
</pre><p>This rule sets the CSS font-size properties for all children of the
               <code>math</code> element that have the <code>mathsize</code> attribute set to small.  
               A MathML renderer
               would then query the style engine for the CSS environment, and use the
               values returned as input to its own layout algorithms.  MathML does
               not specify the mechanism by which style information is inherited from
               the environment.  However, some suggested rendering rules for the
               interaction between properties of the ambient style environment and
               MathML-specific rendering rules are discussed in <a href="chapter3-d.html#presm.commatt">Section&nbsp;3.2.2 Mathematics style attributes common to token elements</a>, and more generally throughout <a href="chapter3-d.html">Chapter&nbsp;3 Presentation Markup</a>.
            </p>
            <p>It should be stressed, however, that some caution is required in
               writing CSS stylesheets for MathML.  Because changing typographic
               properties of mathematics symbols can change the meaning of an equation,
               stylesheets should be written in a way such that changes to document-wide
               typographic styles do not affect embedded MathML expressions.
            </p>
            <p>Another pitfall to be avoided is using CSS to provide
               typographic style information necessary to the proper understanding of
               an expression.
               Expressions dependent on CSS for meaning will not be
               portable to non-CSS environments such as computer algebra systems.  By
               using the logical values of the new MathML 3.0 mathematics style attributes
               as selectors for CSS rules, it can be assured that style information
               necessary to the sense of an expression is encoded directly in the
               MathML.
            </p>
            <p>MathML 3.0 does not specify how a user agent should process style
               information, because there are many non-CSS MathML environments, and
               because different users agents and renderers have widely varying
               degrees of access to CSS information.
            </p>
            <div class="div3">
               
               <h3><a name="id.6.5.1" id="id.6.5.1"></a>6.5.1 Order of processing attributes versus style sheets
               </h3>
               <p>CSS or analogous style sheets can specify changes to rendering
                  properties of selected MathML elements.  Since rendering properties
                  can also be changed by attributes on an element, or be changed
                  automatically by the renderer, it is necessary to specify the order in
                  which changes requested by various sources should occur.
                  The order is defined by <a href="appendixh-d.html#CSS21">[CSS21]</a> cascading order taking into account 
                  precedence of non-CSS presentational hints.
                  
               </p>
            </div>
            <div class="div3">
               
               <h3><a name="id.6.5.2" id="id.6.5.2"></a>6.5.2 Layout engines that lack native MathML support
               </h3>
               <p>
                  While controlling all aspects of MathML formatting through CSS is problematic 
                  and many MathML layout schemata have no analogues in CSS visual formatting model,
                  CSS as a general purpose style language is still capable of formatting representative 
                  subset of MathML. This capability can be used to provide reasonable rendering of MathML
                  in applications that lack native MathML support, but are able to format XML using 
                  a CSS style sheet. More about this possibility and a sample CSS style sheet
                  may be found in <a href="appendixh-d.html#MathMLforCSS">[MathMLforCSS]</a>.
                  
               </p>
            </div>
         </div>
      </div>
      <div class="minitoc">
         
         Overview: <a href="Overview-d.html">Mathematical Markup Language (MathML) Version 3.0</a><br>
         Previous:     5 <a href="chapter5-d.html">Mixing Markup Languages for Mathematical Expressions</a><br>
         Next:     7 <a href="chapter7-d.html">Characters, Entities and Fonts</a></div>
   </body>
</html>