<itemizedlist>
  <listitem id="command_version">
    <para>
      VERSION
      <parameter>number</parameter>
    </para>
    <para>
      This exchanges with the frontend the protocol version number that is
      being used. The current version is 2.1. Versions in the 2.x series
      will be backwards-compatible. You may specify the protocol version
      number you are speaking. The frontend will return the version of the
      protocol it speaks. If the version you specify is too low, this
      command will return the numeric return code <literal>30</literal>.
    </para>
  </listitem>
  <listitem id="command_capb">
    <para>
      CAPB
      <parameter>capabilities</parameter>
    </para>
    <para>
      This exchanges with the frontend a list of supported capabilities
      Capabilities both the frontend and your confmodule support may be
      used; the capabilities supported by the frontend are returned by
      this command.
      <table frame="all">
        <title>Currently used capabilities</title>
        <tgroup cols="2">
          <thead>
            <row>
              <entry>capability</entry>
	      <entry>description</entry>
            </row>
          </thead>
          <tbody>
            <row>
              <entry>backup</entry>
 	      <entry>
	        Backing up to a previous step is supported.
	      </entry>
            </row>
	    <row>
	      <entry>escape</entry>
	      <entry>
	        The frontend expects commands sent to it to have
	        backslashes and newlines quoted as <literal>\\</literal>
	        and <literal>\n</literal> respectively and will in turn
	        quote backslashes and newlines in its replies.  See
	        <citerefentry><refentrytitle>debconf-escape</refentrytitle>
	        <manvolnum>1</manvolnum></citerefentry>.
	      </entry>
	    </row>
	    <row>
	      <entry>multiselect</entry>
	      <entry>
	        The multiselect data type is supported. You do not need to
	        check this capability if you depend on any modern version
	        of debconf.
	      </entry>
	    </row>
          </tbody>
        </tgroup>
      </table>
    </para>
  </listitem>
  <listitem id="command_settitle">
    <para>
      SETTITLE
      <parameter>template</parameter>
    </para>
    <para>
      You can use this command to set a title in the frontend. This may
      appear in different ways, depending on the frontend being used, for
      example it might change the title of the frontend's window. If you
      don't specify anything, a title will automatically be generated.
    </para>
    <para>
      Using a template has the advantage that titles are translatable and
      that they can be maintained in the same place as other text
      displayed to users.
    </para>
  </listitem>
  <listitem id="command_title">
    <para>
      TITLE
      <parameter>string</parameter>
    </para>
    <para>
      Similar to SETTITLE, but takes a string instead of a template as
      parameter. Consequence is that the title will not be translatable,
      unless some other mechanism (like gettext) is used.
    </para>
  </listitem>
  <listitem id="command_stop">
    <para>
      STOP
    </para>
    <para>
      This command tells the frontend you're done talking to it. Typically
      the frontend can detect the termination of your program and this
      command is not necessary.
    </para>
  </listitem>
  <listitem id="command_input">
    <para>
      INPUT
      <parameter>priority</parameter>
      <parameter>question</parameter>
    </para>
    <para>
      This tells the frontend to display a question (or other type of
      item) to the user. <parameter>question</parameter> is the name of
      the item to display, all other information about the item is
      retrieved from the templates described previously.
      <parameter>priority</parameter> is how important it is that the user
      be prompted. The frontend need only ask this question if the
      priority is high enough. The question is not displayed until a go
      command is given. This allows us to ask multiple questions in a
      single screen. Once a question has been displayed to the user and
      the user has provided input, the frontend will set the
      <literal>seen</literal> flag.
      &priority_table;
    </para>
    <para>
      Note that the frontend decides if the user is actually prompted or
      not. If the user has already answered a question, they are normally
      not asked it again even if input is called again. And if the user is
      ignoring low priority items, they will not see them. In either of
      these cases, this command returns the numeric return code
      <literal>30</literal>.
    </para>
  </listitem>
  <listitem id="command_beginblock">
    <para>
      BEGINBLOCK
    </para>
  </listitem>
  <listitem id="command_endblock">
    <para>
      ENDBLOCK
    </para>
    <para>
      Some frontends are able to display a number of items to the user at
      once. To do this, they need to be given blocks of input commands,
      enclosed in the BEGINBLOCK and ENDBLOCK commands. Blocks can be
      nested and very advanced frontends may use this as a user interface
      hint.
    </para>
    <note>
      <para>
        There is an implicit block around any set of INPUT commands that
        are not enclosed in an explicit block.
      </para>
    </note>
  </listitem>
  <listitem id="command_go">
    <para>
      GO
    </para>
    <para>
      Shows the current set of accumulated items to the user and lets them
      fill in values, etc. If the backup capability is supported and the
      user indicates they want to back up a step, this command returns the
      numeric return code <literal>30</literal>.
    </para>
  </listitem>
  <listitem id="command_clear">
    <para>
      CLEAR
    </para>
    <para>
      Clears the accumulated set of INPUT commands without displaying them
      to the user.
    </para>
  </listitem>
  <listitem id="command_get">
    <para>
      GET <parameter>question</parameter>
    </para>
    <para>
      Ask the frontend to tell you how the user answered a question. The
      value is returned to you.
    </para>
  </listitem>
  <listitem id="command_set">
    <para>
      SET
      <parameter>question</parameter>
      <parameter>value</parameter>
    </para>
    <para>
      Set the answer of a question to a value.
    </para>
  </listitem>
  <listitem id="command_reset">
    <para>
      RESET <parameter>question</parameter>
    </para>
    <para>
      Reset the question to its default value. This includes resetting
      flags to their defaults.
    </para>
  </listitem>
  <listitem id="command_subst">
    <para>
      SUBST
      <parameter>question</parameter>
      <parameter>key</parameter>
      <parameter>value</parameter>
    </para>
    <para>
      Questions (and other items) can have substitutions embedded in their
      descriptions (and, currently in their choices fields). These
      substitutions look like "<literal>${key}</literal>". When the
      question is displayed, the substitutions are replaced with their
      values. This command can be used to set the value of a substitution.
    </para>
  </listitem>
  <listitem id="command_fget">
    <para>
      FGET
      <parameter>question</parameter>
      <parameter>flag</parameter>
    </para>
    <para>
      Questions (and other items) can have flags associated with them. The
      flags have a value of "<literal>true</literal>" or
      "<literal>false</literal>". This command returns the value of a
      flag.
    </para>
  </listitem>
  <listitem id="command_fset">
    <para>
      FSET
      <parameter>question</parameter>
      <parameter>flag</parameter>
      <parameter>value</parameter>
    </para>
    <para>
      This sets the state of a flag on a question. Valid states for the
      flag are "<literal>true</literal>" and "<literal>false</literal>".
    </para>
    <para>
      One common flag is the "<literal>seen</literal>" flag. It is
      normally only set if a user already seen a question.  Typically,
      frontends only display questions to users if they have the seen flag
      set to "false". Sometimes you want the user to see a question again
      -- in these cases you can set the seen flag to false to force the
      frontend to redisplay it.
    </para>
    <para>
      Note that as a special convenience behavior, frontends will
      redisplay already seen questions if the question was first seen by
      the user in the same confmodule run. This makes it easy for a
      confmodule to back up to previous questions without having to reset
      the seen flag.
    </para>
  </listitem>
  <listitem id="command_metaget">
    <para>
      METAGET
      <parameter>question</parameter>
      <parameter>field</parameter>
    </para>
    <para>
      This returns the value of any field of a question (the description,
      for example).
    </para>
  </listitem>
  <listitem id="command_register">
    <para>
      REGISTER
      <parameter>template</parameter>
      <parameter>question</parameter>
    </para>
    <para>
      This creates a new question that is bound to a template. By default
      each template has an associated question with the same
      name. However, any number of questions can really be associated with
      a template, and this lets you create more such questions.
    </para>
  </listitem>
  <listitem id="command_unregister">
    <para>
      UNREGISTER
      <parameter>question</parameter>
    </para>
    <para>
      This removes a question from the database.
    </para>
  </listitem>
  <listitem id="command_purge">
    <para>
      PURGE
    </para>
    <para>
      Call this in your postrm when your package is purged. It removes all
      templates and questions your package has generated.
    </para>
  </listitem>
</itemizedlist>