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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<head>
<title>Boost.Regex: Perl Regular Expression Syntax</title>
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<P>
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<TR>
<td vAlign="top" width="300">
<h3><A href="../../../index.htm"><IMG height="86" alt="C++ Boost" src="../../../boost.png" width="277" border="0"></A></h3>
</td>
<TD width="353">
<H1 align="center">Boost.Regex</H1>
<H2 align="center">
Perl Regular Expression Syntax</H2>
</TD>
<td width="50">
<h3><A href="index.html"><IMG height="45" alt="Boost.Regex Index" src="uarrow.gif" width="43" border="0"></A></h3>
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<HR>
<H3>Contents</H3>
<dl class="index">
<dt><A href="#synopsis">Synopsis</A> <dt><A href="#Perl">Perl Syntax</A> <dt><A href="#what">
What Gets Matched</A> <dt><A href="#variations">Variations</A>
<dd>
<dt><A href="#options">Options</A> <dt><A href="#mods">Modifiers</A> <dt><A href="#refs">References</A></dt>
</dl>
<H3><A name="synopsis"></A>Synopsis</H3>
<P>The Perl regular expression syntax is based on that used by the programming
language <EM>Perl</EM> . Perl regular expressions are the default
behavior in Boost.Regex or you can pass the flag <EM>perl</EM> to the
regex constructor, for example:</P>
<PRE>// e1 is a case sensitive Perl regular expression:
// since Perl is the default option there's no need to explicitly specify the syntax used here:
boost::regex e1(my_expression);
// e2 a case insensitive Perl regular expression:
boost::regex e2(my_expression, boost::regex::perl|boost::regex::icase);</PRE>
<H3>Perl Regular Expression Syntax<A name="Perl"></A></H3>
<P>In Perl regular expressions, all characters match themselves except for
the following special characters:</P>
<PRE>.[{()\*+?|^$</PRE>
<H4>Wildcard:</H4>
<P>The single character '.' when used outside of a character set will match any
single character except:</P>
<P>The NULL character when the flag <EM>match_no_dot_null</EM> is passed to the
matching algorithms.</P>
<P>The newline character when the flag <EM>match_not_dot_newline</EM> is passed to
the matching algorithms.</P>
<H4>Anchors:</H4>
<P>A '^' character shall match the start of a line.</P>
<P>A '$' character shall match the end of a line.</P>
<H4>Marked sub-expressions:</H4>
<P>A section beginning ( and ending ) acts as a marked sub-expression.
Whatever matched the sub-expression is split out in a separate field by the
matching algorithms. Marked sub-expressions can also repeated, or
referred to by a back-reference.</P>
<H4>Non-marking grouping:</H4>
<P>A marked sub-expression is useful to lexically group part of a regular
expression, but has the side-effect of spitting out an extra field in the
result. As an alternative you can lexically group part of a regular
expression, without generating a marked sub-expression by using (?: and ) , for
example (?:ab)+ will repeat "ab" without splitting out any separate
sub-expressions.</P>
<H4>Repeats:</H4>
<P>Any atom (a single character, a marked sub-expression, or a character class)
can be repeated with the *, +, ?, and {} operators.</P>
<P>The * operator will match the preceding atom zero or more times, for example
the expression a*b will match any of the following:</P>
<PRE>b
ab
aaaaaaaab</PRE>
<P>The + operator will match the preceding atom one or more times, for example the
expression a+b will match any of the following:</P>
<PRE>ab
aaaaaaaab</PRE>
<P>But will not match:</P>
<PRE>b</PRE>
<P>The ? operator will match the preceding atom zero or one times, for
example the expression ca?b will match any of the following:</P>
<PRE>cb
cab</PRE>
<P>But will not match:</P>
<PRE>caab</PRE>
<P>An atom can also be repeated with a bounded repeat:</P>
<P>a{n} Matches 'a' repeated exactly <EM>n</EM> times.</P>
<P>a{n,} Matches 'a' repeated <EM>n</EM> or more times.</P>
<P>a{n, m} Matches 'a' repeated between <EM>n</EM> and <EM>m</EM> times
inclusive.</P>
<P>For example:</P>
<PRE>^a{2,3}$</PRE>
<P>Will match either of:</P>
<PRE>aa
aaa</PRE>
<P>But neither of:</P>
<PRE>a
aaaa</PRE>
<P>It is an error to use a repeat operator, if the preceding construct can not be
repeated, for example:</P>
<PRE>a(*)</PRE>
<P>Will raise an error, as there is nothing for the * operator to be applied to.</P>
<H4>Non greedy repeats</H4>
<P>The normal repeat operators are "greedy", that is to say they will consume as
much input as possible. There are non-greedy versions available that will
consume as little input as possible while still producing a match.</P>
<P>*? Matches the previous atom zero or more times, while consuming as little
input as possible.</P>
<P>+? Matches the previous atom one or more times, while consuming as little input
as possible.</P>
<P>?? Matches the previous atom zero or one times, while consuming as little input
as possible.</P>
<P>{n,}? Matches the previous atom <EM>n</EM> or more times, while consuming
as little input as possible.</P>
<P>{n,m}? Matches the previous atom between <EM>n</EM> and <EM>m</EM> times,
while consuming as little input as possible.</P>
<H4>Back references:</H4>
<P>An escape character followed by a digit <EM>n</EM>, where <EM>n </EM>is in the
range 1-9, matches the same string that was matched by sub-expression <EM>n</EM>.
For example the expression:</P>
<PRE>^(a*).*\1$</PRE>
<P>Will match the string:</P>
<PRE>aaabbaaa</PRE>
<P>But not the string:</P>
<PRE>aaabba</PRE>
<H4>Alternation</H4>
<P>The | operator will match either of its arguments, so for example: abc|def will
match either "abc" or "def".
</P>
<P>Parenthesis can be used to group alternations, for example: ab(d|ef) will match
either of "abd" or "abef".</P>
<P>Empty alternatives are not allowed (these are almost always a mistake),
but if you really want an empty alternative use (?:) as a placeholder, for
example:</P>
<BLOCKQUOTE dir="ltr" style="MARGIN-RIGHT: 0px">
<P>"|abc" is not a valid expression, but<BR>
"(?:)|abc" is and is equivalent, also the expression:<BR>
"(?:abc)??" has exactly the same effect.</P>
</BLOCKQUOTE>
<H4>Character sets:</H4>
<P>A character set is a bracket-expression starting with [ and ending with ], it
defines a set of characters, and matches any single character that is a member
of that set.</P>
<P>A bracket expression may contain any combination of the following:</P>
<BLOCKQUOTE dir="ltr" style="MARGIN-RIGHT: 0px">
<H5>Single characters:</H5>
<P>For example [abc], will match any of the characters 'a', 'b', or 'c'.</P>
<H5>Character ranges:</H5>
<P>For example [a-c] will match any single character in the range 'a' to
'c'. By default, for POSIX-Perl regular expressions, a character <EM>x</EM>
is within the range <EM>y</EM> to <EM>z</EM>, if it collates within that
range; this results in locale specific behavior. This behavior can
be turned off by unsetting the <EM><A href="syntax_option_type.html#Perl">collate</A></EM>
option flag - in which case whether a character appears within a range is
determined by comparing the code points of the characters only</P>
<H5>Negation:</H5>
<P>If the bracket-expression begins with the ^ character, then it matches the
complement of the characters it contains, for example [^a-c] matches any
character that is not in the range a-c.</P>
<H5>Character classes:</H5>
<P>An expression of the form [[:name:]] matches the named character class "name",
for example [[:lower:]] matches any lower case character. See <A href="character_class_names.html">
character class names</A>.</P>
<H5>Collating Elements:</H5>
<P>An expression of the form [[.col.] matches the collating element <EM>col</EM>.
A collating element is any single character, or any sequence of characters that
collates as a single unit. Collating elements may also be used as the end
point of a range, for example: [[.ae.]-c] matches the character sequence "ae",
plus any single character in the range "ae"-c, assuming that "ae" is treated as
a single collating element in the current locale.</P>
<P>As an extension, a collating element may also be specified via it's <A href="collating_names.html">
symbolic name</A>, for example:</P>
<P>[[.NUL.]]</P>
<P>matches a NUL character.</P>
<H5>Equivalence classes:</H5>
<P>
An expression oftheform[[=col=]], matches any character or collating element
whose primary sort key is the same as that for collating element <EM>col</EM>,
as with colating elements the name <EM>col</EM> may be a <A href="collating_names.html">
symbolic name</A>. A primary sort key is one that ignores case,
accentation, or locale-specific tailorings; so for example [[=a=]] matches any
of the characters: a, , , , , , , A, , , , , and .
Unfortunately implementation of this is reliant on the platform's collation and
localisation support; this feature can not be relied upon to work portably
across all platforms, or even all locales on one platform.</P>
<H5>Escapes:</H5>
<P>All the escape sequences that match a single character, or a single character
class are permitted within a character class definition, <EM>except</EM> the
negated character classes (\D \W etc).</P>
</BLOCKQUOTE>
<H5>Combinations:</H5>
<P>All of the above can be combined in one character set declaration, for example:
[[:digit:]a-c[.NUL.]].</P>
<H4>Escapes</H4>
<P>Any special character preceded by an escape shall match itself.
</P>
<P>The following escape sequences are also supported:</P>
<BLOCKQUOTE dir="ltr" style="MARGIN-RIGHT: 0px">
<H5>Escapes matching a specific character</H5>
<P>The following escape sequences are all synonyms for single characters:</P>
<P>
<TABLE id="Table7" cellSpacing="1" cellPadding="1" width="100%" border="1">
<TR>
<TD><STRONG>Escape</STRONG></TD>
<TD><STRONG>Character</STRONG></TD>
</TR>
<TR>
<TD>\a</TD>
<TD>'\a'</TD>
</TR>
<TR>
<TD>\e</TD>
<TD>0x1B</TD>
</TR>
<TR>
<TD>\f</TD>
<TD>\f</TD>
</TR>
<TR>
<TD>\n</TD>
<TD>\n</TD>
</TR>
<TR>
<TD>\r</TD>
<TD>\r</TD>
</TR>
<TR>
<TD>\t</TD>
<TD>\t</TD>
</TR>
<TR>
<TD>\v</TD>
<TD>\v</TD>
</TR>
<TR>
<TD>\b</TD>
<TD>\b (but only inside a character class declaration).</TD>
</TR>
<TR>
<TD>\cX</TD>
<TD>An ASCII escape sequence - the character whose code point is X % 32</TD>
</TR>
<TR>
<TD>\xdd</TD>
<TD>A hexadecimal escape sequence - matches the single character whose code point
is 0xdd.</TD>
</TR>
<TR>
<TD>\x{dddd}</TD>
<TD>A hexadecimal escape sequence - matches the single character whose code point
is 0xdddd.</TD>
</TR>
<TR>
<TD>\0ddd</TD>
<TD>An octal escape sequence - matches the single character whose code point is
0ddd.</TD>
</TR>
<TR>
<TD>\N{name}</TD>
<TD>Matches the single character which has the <A href="collating_names.html">symbolic
name</A> <EM>name. </EM>For example \N{newline} matches the single
character \n.</TD>
</TR>
</TABLE>
</P>
<H5>"Single character" character classes:</H5>
<P>Any escaped character <EM>x</EM>, if <EM>x</EM> is the name of a character
class shall match any character that is a member of that class, and any escaped
character <EM>X</EM>, if <EM>x</EM> is the name of a character class, shall
match any character not in that class.</P>
<P>The following are supported by default:</P>
<P>
<TABLE id="Table3" cellSpacing="1" cellPadding="1" width="300" border="1">
<TR>
<TD><STRONG>Escape sequence</STRONG></TD>
<TD><STRONG>Equivalent to</STRONG></TD>
</TR>
<TR>
<TD>\d</TD>
<TD>[[:digit:]]</TD>
</TR>
<TR>
<TD>\l</TD>
<TD>[[:lower:]]</TD>
</TR>
<TR>
<TD>\s</TD>
<TD>[[:space:]]</TD>
</TR>
<TR>
<TD>\u</TD>
<TD>[[:upper:]]</TD>
</TR>
<TR>
<TD>\w</TD>
<TD>[[:word:]]</TD>
</TR>
<TR>
<TD>\D</TD>
<TD>[^[:digit:]]</TD>
</TR>
<TR>
<TD>\L</TD>
<TD>[^[:lower:]]</TD>
</TR>
<TR>
<TD>\S</TD>
<TD>[^[:space:]]</TD>
</TR>
<TR>
<TD>\U</TD>
<TD>[^[:upper:]]</TD>
</TR>
<TR>
<TD>\W</TD>
<TD>[^[:word:]]</TD>
</TR>
</TABLE>
</P>
<H5>Character Properties</H5>
<P>The character property names in the following table are all equivalent to the <A href="character_class_names.html">
names used in character classes</A>.</P>
<P>
<TABLE id="Table9" cellSpacing="1" cellPadding="1" width="100%" border="0">
<TR>
<TD><STRONG>Form</STRONG></TD>
<TD><STRONG>Description</STRONG></TD>
<TD><STRONG>Equivalent character set form</STRONG></TD>
</TR>
<TR>
<TD>\pX</TD>
<TD>Matches any character that has the property X.</TD>
<TD>[[:X:]]</TD>
</TR>
<TR>
<TD>\p{Name}</TD>
<TD>Matches any character that has the property <EM>Name</EM>.</TD>
<TD>[[:Name:]]</TD>
</TR>
<TR>
<TD>\PX</TD>
<TD>Matches any character that does not have the property X.</TD>
<TD>[^[:X:]]</TD>
</TR>
<TR>
<TD>\P{Name}</TD>
<TD>Matches any character that does not have the property <EM>Name</EM>.</TD>
<TD>[^[:Name:]]</TD>
</TR>
</TABLE>
</P>
<H5>Word Boundaries</H5>
<P>The following escape sequences match the boundaries of words:</P>
<P>
<TABLE id="Table4" cellSpacing="1" cellPadding="1" width="100%" border="1">
<TR>
<TD>\<</TD>
<TD>Matches the start of a word.</TD>
</TR>
<TR>
<TD>\></TD>
<TD>Matches the end of a word.</TD>
</TR>
<TR>
<TD>\b</TD>
<TD>Matches a word boundary (the start or end of a word).</TD>
</TR>
<TR>
<TD>\B</TD>
<TD>Matches only when not at a word boundary.</TD>
</TR>
</TABLE>
</P>
<H5>Buffer boundaries</H5>
<P>The following match only at buffer boundaries: a "buffer" in this context is
the whole of the input text that is being matched against (note that ^ and
$ may match embedded newlines within the text).</P>
<P>
<TABLE id="Table5" cellSpacing="1" cellPadding="1" width="100%" border="1">
<TR>
<TD>\`</TD>
<TD>Matches at the start of a buffer only.</TD>
</TR>
<TR>
<TD>\'</TD>
<TD>Matches at the end of a buffer only.</TD>
</TR>
<TR>
<TD>\A</TD>
<TD>Matches at the start of a buffer only (the same as \`).</TD>
</TR>
<TR>
<TD>\z</TD>
<TD>Matches at the end of a buffer only (the same as \').</TD>
</TR>
<TR>
<TD>\Z</TD>
<TD>Matches an optional sequence of newlines at the end of a buffer: equivalent to
the regular expression \n*\z</TD>
</TR>
</TABLE>
</P>
<H5>Continuation Escape</H5>
<P>The sequence \G matches only at the end of the last match found, or at the
start of the text being matched if no previous match was found. This
escape useful if you're iterating over the matches contained within a text, and
you want each subsequence match to start where the last one ended.</P>
<H5>Quoting escape</H5>
<P>The escape sequence \Q begins a "quoted sequence": all the subsequent
characters are treated as literals, until either the end of the regular
expression or \E is found. For example the expression: \Q\*+\Ea+ would
match either of:</P>
<PRE>\*+a<BR>\*+aaa</PRE>
<H5>Unicode escapes</H5>
<P>
<TABLE id="Table6" cellSpacing="1" cellPadding="1" width="100%" border="1">
<TR>
<TD>\C</TD>
<TD>Matches a single code point: in Boost regex this has exactly the same effect
as a "." operator.</TD>
</TR>
<TR>
<TD>\X</TD>
<TD>Matches a combining character sequence: that is any non-combining character
followed by a sequence of zero or more combining characters.</TD>
</TR>
</TABLE>
</P>
<H5>Any other escape</H5>
<P>Any other escape sequence matches the character that is escaped, for example \@
matches a literal <A href="mailto:'@'">'@'</A>.</P>
</BLOCKQUOTE>
<H4 dir="ltr">Perl Extended Patterns</H4>
<P dir="ltr">Perl-specific extensions to the regular expression syntax all start
with (?.</P>
<BLOCKQUOTE dir="ltr" style="MARGIN-RIGHT: 0px">
<H5 dir="ltr">Comments</H5>
<P dir="ltr">(?# ... ) is treated as a comment, it's contents are ignored.</P>
<H5 dir="ltr">Modifiers</H5>
<P dir="ltr">(?imsx-imsx ... ) alters which of the perl modifiers are in effect
within the pattern, changes take effect from the point that the block is first
seen and extend to any enclosing ). Letters before a '-' turn that perl
modifier on, letters afterward, turn it off.</P>
<P dir="ltr">(?imsx-imsx:pattern) applies the specified modifiers to <EM>pattern</EM>
only.</P>
<H5 dir="ltr">Non-marking grouping</H5>
<P dir="ltr">(?:pattern) lexically groups <EM>pattern</EM>, without generating an
additional sub-expression.</P>
<H5 dir="ltr">Lookahead</H5>
<P dir="ltr">(?=pattern) consumes zero characters, only if <EM>pattern</EM> matches.</P>
<P dir="ltr">(?!pattern) consumes zero characters, only if <EM>pattern</EM> does
not match.</P>
<P dir="ltr">Lookahead is typically used to create the logical AND of two regular
expressions, for example if a password must contain a lower case letter, an
upper case letter, a punctuation symbol, and be at least 6 characters long,
then the expression:</P>
<PRE dir="ltr">(?=.*[[:lower:]])(?=.*[[:upper:]])(?=.*[[:punct:]]).{6,}</PRE>
<P dir="ltr">could be used to validate the password.</P>
<H5 dir="ltr">Lookbehind</H5>
<P dir="ltr">(?<=pattern) consumes zero characters, only if <EM>pattern</EM> could
be matched against the characters preceding the current position (<EM>pattern</EM>
must be of fixed length).</P>
<P dir="ltr">(?<!pattern) consumes zero characters, only if <EM>pattern</EM> could
not be matched against the characters preceding the current position (<EM>pattern</EM>
must be of fixed length).</P>
<H5 dir="ltr">Independent sub-expressions</H5>
<P dir="ltr">(?>pattern) <EM>pattern</EM> is matched independently of the
surrounding patterns, the expression will never backtrack into <EM>pattern</EM>.
Independent sub-expressions are typically used to improve performance; only the
best possible match for <EM>pattern</EM> will be considered, if this doesn't
allow the expression as a whole to match then no match is found at all.</P>
<H5 dir="ltr">Conditional Expressions</H5>
<P dir="ltr">(?(condition)yes-pattern|no-pattern) attempts to match <EM>yes-pattern</EM>
if the <EM>condition </EM>is true, otherwise attempts to match <EM>no-pattern</EM>.</P>
<P dir="ltr">(?(condition)yes-pattern) attempts to match <EM>yes-pattern</EM> if
the <EM>condition </EM>is true, otherwise fails.</P>
<P dir="ltr"><EM>Condition</EM> may be either a forward lookahead assert, or the
index of a marked sub-expression (the condition becomes true if the
sub-expression has been matched).</P>
</BLOCKQUOTE><A name="what">
<H4>Operator precedence</H4>
<P> The order of precedence for of operators is as shown in the following
table:</P>
<P>
<TABLE id="Table2" cellSpacing="1" cellPadding="1" width="100%" border="1">
<TR>
<TD>Collation-related bracket symbols</TD>
<TD>[==] [::] [..]</TD>
</TR>
<TR>
<TD>Escaped characters
</TD>
<TD>\</TD>
</TR>
<TR>
<TD>Character set (bracket expression)
</TD>
<TD>[]</TD>
</TR>
<TR>
<TD>Grouping</TD>
<TD>()</TD>
</TR>
<TR>
<TD>Single-character-ERE duplication
</TD>
<TD>* + ? {m,n}</TD>
</TR>
<TR>
<TD>Concatenation</TD>
<TD></TD>
</TR>
<TR>
<TD>Anchoring</TD>
<TD>^$</TD>
</TR>
<TR>
<TD>Alternation</TD>
<TD>|</TD>
</TR>
</TABLE>
</P>
</A>
<H3>What gets matched</H3>
<P>If you view the regular expression as a directed (possibly cyclic) graph, then
the best match found is the first match found by a depth-first-search performed
on that graph, while matching the input text.</P>
<P>Alternatively:</P>
<P>the best match found is the leftmost match, with individual elements matched as
follows;</P>
<P>
<TABLE id="Table8" cellSpacing="1" cellPadding="1" width="100%" border="0">
<TR>
<TD><STRONG>Construct</STRONG></TD>
<TD><STRONG>What gets matches</STRONG></TD>
</TR>
<TR>
<TD>AtomA AtomB</TD>
<TD>Locates the best match for AtomA that has a following match for AtomB.</TD>
</TR>
<TR>
<TD>Expression1 | Expression2</TD>
<TD>If Expresion1 can be matched then returns that match, otherwise attempts to
match Expression2.</TD>
</TR>
<TR>
<TD>S{N}</TD>
<TD>Matches S repeated exactly N times.</TD>
</TR>
<TR>
<TD>S{N,M}</TD>
<TD>Matches S repeated between N and M times, and as many times as possible.</TD>
</TR>
<TR>
<TD>S{N,M}?</TD>
<TD>Matches S repeated between N and M times, and as few times as possible.</TD>
</TR>
<TR>
<TD><!--StartFragment --> S?, S*, S+</TD>
<TD><!--StartFragment --> The same as <CODE>S{0,1}</CODE>, <CODE>S{0,UINT_MAX}</CODE>,
<CODE>S{1,UINT_MAX}</CODE> respectively.
</TD>
</TR>
<TR>
<TD>S??, S*?, S+?</TD>
<TD>The same as <CODE>S{0,1}?</CODE>, <CODE>S{0,UINT_MAX}?</CODE>, <CODE>S{1,UINT_MAX}?</CODE>
respectively.
</TD>
</TR>
<TR>
<TD><!--StartFragment --> (?>S)
</TD>
<TD>Matches the best match for S, and only that.</TD>
</TR>
<TR>
<TD>
(?=S), (?<=S)
</TD>
<TD>Matches only the best match for S (this is only visible if there are capturing
parenthesis within S).</TD>
</TR>
<TR>
<TD><!--StartFragment --> (?!S), (?<!S)</TD>
<TD>Considers only whether a match for S exists or not.</TD>
</TR>
<TR>
<TD><!--StartFragment --> (?(condition)yes-pattern | no-pattern)</TD>
<TD>If condition is <EM>true</EM>, then only <EM>yes-pattern</EM> is considered,
otherwise only <EM>no-pattern</EM> is considered.</TD>
</TR>
</TABLE>
</P>
<H3><A name="variations"></A>Variations</H3>
<P>The options <A href="syntax_option_type.html#perl"><EM>normal, ECMAScript, JavaScript</EM>
and <EM>JScript</EM></A> are all synonyms for <EM>Perl</EM>.</P>
<H3><A name="options"></A>Options</H3>
<P>There are a <A href="syntax_option_type.html#Perl">variety of flags</A> that
may be combined with the <EM>Perl</EM> option when constructing the regular
expression, in particular note that the <A href="syntax_option_type.html#Perl">newline_alt</A>
option alters the syntax, while the <A href="syntax_option_type.html#Perl">collate,
nosubs and icase</A> options modify how the case and locale sensitivity
are to be applied.</P>
<H3><A name="mods"></A>Modifiers</H3>
<P>The perl <EM>smix</EM> modifiers can either be applied using a (?smix-smix)
prefix to the regular expression, or with one of the regex-compile time flags <EM><A href="syntax_option_type.html#Perl">
no_mod_m, mod_x, mod_s, and no_mod_s</A></EM>.
</P>
<H3><A name="refs">References</H3>
<P><A href="http://perldoc.perl.org/perlre.html"> Perl 5.8.</A></P>
<HR>
<P></P>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
21 Aug 2004
<!--webbot bot="Timestamp" endspan i-checksum="39359" --></p>
<P><I> Copyright <a href="mailto:jm@regex.fsnet.co.uk">John Maddock</a> 2004</I></P>
<I>
<P><I>Use, modification and distribution are subject to the Boost Software License,
Version 1.0. (See accompanying file <A href="../../../LICENSE_1_0.txt">LICENSE_1_0.txt</A>
or copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>).</I></P>
</I>
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