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  • Author : matthieu
    Date : 2015-04-06 20:57:55
    Hash : 8252bb00
    Message : update to libX11 1.6.3

  • lib/libX11/specs/XKB/ch02.xml
  • <?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
    	  "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd">
    <chapter id='Initialization_and_General_Programming_Information'>
    <title>Initialization and General Programming Information</title>
    <sect1 id='Extension_Header_Files'>
    <title>Extension Header Files</title>
    <para>
    The following include files are part of the Xkb standard:
    </para>
    <itemizedlist>
      <listitem>
        <para>
    <filename class="headerfile">&lt;X11/XKBlib.h&gt;</filename>
        </para>
        <para><filename class="headerfile">XKBlib.h</filename>
    is the main header file for Xkb; it declares constants, types, and
    functions.
        </para>
      </listitem>
      <listitem>
        <para>
    <filename class="headerfile">&lt;X11/extensions/XKBstr.h&gt;</filename>
        </para>
        <para>
    <filename class="headerfile">XKBstr.h</filename> declares types and
    constants for Xkb. It is included automatically from
    <filename class="headerfile">&lt;X11/XKBlib.h&gt;</filename>;
    you should never need to reference it directly in your application code.
        </para>
      </listitem>
      <listitem>
        <para>
    <filename class="headerfile">&lt;X11/extensions/XKB.h&gt;</filename>
        </para>
        <para>
    <filename class="headerfile">XKB.h</filename>
    defines constants for Xkb. It is included automatically from
    <filename class="headerfile">&lt;X11/XKBstr.h&gt;</filename>;
    you should never need to reference it directly in your application code.
        </para>
      </listitem>
      <listitem>
        <para>
    <filename class="headerfile">&lt;X11/extensions/XKBgeom.h&gt;</filename>
       </para>
       <para><filename class="headerfile">XKBgeom.h</filename>
    declares types, symbolic constants, and functions for manipulating
    keyboard geometry descriptions.
        </para>
      </listitem>
    </itemizedlist>
    </sect1>
    <sect1 id='Extension_Name'>
    <title>Extension Name</title>
    <indexterm significance="preferred" zone="Extension_Name"><primary><symbol>XkbName</symbol></primary></indexterm>
    <para>
    The name of the Xkb extension is given in
    <filename class="headerfile">&lt;X11/extensions/Xkb.h&gt;</filename>:
    
    <programlisting>
    #define XkbName "XKEYBOARD"
    </programlisting>
    </para>
    
    <para>
    Most extensions to the X protocol are initialized by calling
    <function>XInitExtension</function>
    and passing the extension name. However, as explained in <link linkend="Initializing_the_Keyboard_Extension">section 2.4</link>, Xkb
    requires a more complex initialization sequence, and a client program should
    not call
    <function>XInitExtension</function>
    directly.
    </para>
    </sect1>
    <sect1 id='Determining_Library_Compatibility'>
    <title>Determining Library Compatibility</title>
    <para>
    If an application is dynamically linked, both the X server and the client-side
    X library must contain the Xkb extension in order for the client to use the Xkb
    extension capabilities. Therefore a dynamically linked application must check
    both the library and the server for compatibility before using Xkb function
    calls. A properly written program must check for compatibility between the
    version of the Xkb library that is dynamically loaded and the one used when the
    application was built. It must then check the server version for compatibility
    with the version of Xkb in the library.
    </para>
    <para>
    If your application is statically linked, you must still check for server
    compatibility and may check library compatibility. (It is possible to compile
    against one set of header files and link against a different, incompatible,
    version of the library, although this should not normally occur.)
    </para>
    <para>
    To determine the compatibility of a library at runtime, call
    <function>XkbLibraryVersion</function>.
    </para>
    <indexterm significance="preferred" zone="XkbLibraryVersion"><primary><function>XkbLibraryVersion</function></primary></indexterm>
    <funcsynopsis id="XkbLibraryVersion">
      <funcprototype>
        <funcdef>Bool <function>XkbLibraryVersion</function></funcdef>
    <!-- (
    <parameter>lib_major_in_out</parameter>,
    <parameter>lib_minor_in_out</parameter>
    ) -->
    
        <paramdef>int *<parameter>lib_major_in_out</parameter></paramdef>
        <paramdef>int *<parameter>lib_minor_in_out</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
    <variablelist>
      <varlistentry>
        <term>
          <parameter>lib_major_in_out</parameter>
        </term>
        <listitem>
          <para>
            specifies and returns the major Xkb library version.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>lib_minor_in_out</parameter>
        </term>
        <listitem>
          <para>
            specifies and returns the minor Xkb library version.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
    
    <para>
    Pass the symbolic value
    <symbol>XkbMajorVersion</symbol>
    in
    <parameter>lib_major_in_out</parameter>
    and
    <symbol>XkbMinorVersion</symbol>
    in
    <parameter>lib_minor_in_out</parameter>.
    These arguments represent the version of the library used at compile time.
    The
    <function>XkbLibraryVersion</function>
    function backfills the major and minor version numbers of the library used at
    run time in
    <parameter>lib_major_in_out</parameter>
    and
    <parameter>lib_minor_in_out</parameter>.
    If the versions of the compile time and run time libraries are compatible,
    <function>XkbLibraryVersion</function>
    returns
    <symbol>True</symbol>,
    otherwise, it returns
    <symbol>False</symbol>.
    </para>
    
    <para>
    In addition, in order to use the Xkb extension, you must ensure that the
    extension is present in the server and that the server supports the version of
    the extension expected by the client. Use
    <function>XkbQueryExtension</function>
    to do this, as described in the next section.
    </para>
    
    </sect1>
    <sect1 id='Initializing_the_Keyboard_Extension'>
    <title>Initializing the Keyboard Extension</title>
    <para>
    Call
    <function>XkbQueryExtension</function>
    to check for the presence and compatibility of the extension in the server and
    to initialize the extension. Because of potential version mismatches, you
    cannot use the generic extension mechanism functions
    (<function>XQueryExtension</function>
    and
    <function>XInitExtension</function>)
    for checking for the presence of, and initializing the Xkb extension.
    </para>
    
    <para>
    You must call
    <function>XkbQueryExtension</function>
    or
    <function>XkbOpenDisplay</function>
    before using any other Xkb library interfaces, unless such usage is explicitly
    allowed in the interface description in this document. The exceptions are:
    <function>XkbIgnoreExtension</function>,
    <function>XkbLibraryVersion</function>,
    and a handful of audible-bell functions. You should not use any other Xkb
    functions if the extension is not present or is uninitialized. In general,
    calls to Xkb library functions made prior to initializing the Xkb extension
    cause
    <errorname>BadAccess</errorname>
    protocol errors.
    <indexterm zone="Initializing_the_Keyboard_Extension"><primary>errors</primary>
    <secondary><errorname>BadAccess</errorname></secondary></indexterm>
    <indexterm zone="Initializing_the_Keyboard_Extension">
    <primary><errorname>BadAccess</errorname></primary></indexterm>
    </para>
    
    <para>
    <function>XkbQueryExtension</function>
    both determines whether a compatible Xkb extension is present in the X server
    and initializes the extension when it is present.
    </para>
    
    <indexterm significance="preferred" zone="XkbQueryExtension"><primary><function>XkbQueryExtension</function></primary></indexterm>
    <funcsynopsis id="XkbQueryExtension">
      <funcprototype>
        <funcdef>Bool <function>XkbQueryExtension</function></funcdef>
    <!-- (
    <parameter>dpy, opcode_rtrn, event_rtrn, error_rtrn, major_in_out, minor_in_out</parameter>
    ) -->
    
        <paramdef>Display *<parameter>dpy</parameter></paramdef>
        <paramdef>int *<parameter>opcode_rtrn</parameter></paramdef>
        <paramdef>int *<parameter>event_rtrn</parameter></paramdef>
        <paramdef>int *<parameter>error_rtrn</parameter></paramdef>
        <paramdef>int *<parameter>major_in_out</parameter></paramdef>
        <paramdef>int *<parameter>minor_in_out</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
    <variablelist>
      <varlistentry>
        <term>
          <parameter>dpy</parameter>
        </term>
        <listitem>
          <para>
            connection to the X server
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>opcode_rtrn</parameter>
        </term>
        <listitem>
          <para>
            backfilled with the major extension opcode
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>event_rtrn</parameter>
        </term>
        <listitem>
          <para>
            backfilled with the extension base event code
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>error_rtrn</parameter>
        </term>
        <listitem>
          <para>
            backfilled with the extension base error code
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>major_in_out</parameter>
        </term>
        <listitem>
          <para>
            compile time lib major version in, server major version out
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>minor_in_out</parameter>
        </term>
        <listitem>
          <para>
            compile time lib min version in, server minor version out
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
    
    <para>
    The
    <function>XkbQueryExtension</function>
    function determines whether a compatible version of the X Keyboard Extension
    is present in the server. If a compatible extension is present,
    <function>XkbQueryExtension</function>
    returns
    <symbol>True</symbol>;
    otherwise, it returns
    <symbol>False</symbol>.
    </para>
    
    <para>
    If a compatible version of Xkb is present,
    <function>XkbQueryExtension</function>
    initializes the extension. It backfills the major opcode for the keyboard
    extension in
    <parameter>opcode_rtrn</parameter>,
    the base event code in
    <parameter>event_rtrn</parameter>,
    the base error code in
    <parameter>error_rtrn</parameter>,
    and the major and minor version numbers of the extension in
    <parameter>major_in_out</parameter>
    and
    <parameter>minor_in_out</parameter>.
    The major opcode is reported in the
    <structfield>req_major</structfield>
    fields of some Xkb events. For a discussion of the base event code, see
    <link linkend="Xkb_Event_Types">section 4.1</link>.
    </para>
    
    <para>
    As a convenience, you can use the function
    <function>XkbOpenDisplay</function>
    to perform these three tasks at once: open a connection to an X server, check
    for a compatible version of the Xkb extension in both the library and the
    server, and initialize the extension for use.
    </para>
    
    <indexterm significance="preferred" zone="XkbOpenDisplay"><primary><function>XkbOpenDisplay</function></primary></indexterm>
    <funcsynopsis id="XkbOpenDisplay">
      <funcprototype>
        <funcdef>Display *<function>XkbOpenDisplay</function></funcdef>
    <!-- (
    <parameter>display_name, event_rtrn, error_rtrn, major_in_out, minor_in_out,
    reason_rtrn)</parameter> -->
    
        <paramdef>char *<parameter>display_name</parameter></paramdef>
        <paramdef>int *<parameter>event_rtrn</parameter></paramdef>
        <paramdef>int *<parameter>error_rtrn</parameter></paramdef>
        <paramdef>int *<parameter>major_in_out</parameter></paramdef>
        <paramdef>int *<parameter>minor_in_out</parameter></paramdef>
        <paramdef>int *<parameter>reason_rtrn</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
    <variablelist>
      <varlistentry>
        <term>
          <parameter>display_name</parameter>
        </term>
        <listitem>
          <para>
            hardware display name, which determines the display and
            communications domain to be used
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>event_rtrn</parameter>
        </term>
        <listitem>
          <para>
            backfilled with the extension base event code
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>error_rtrn</parameter>
        </term>
        <listitem>
          <para>
            backfilled with the extension base error code
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>major_in_out</parameter>
        </term>
        <listitem>
          <para>
            compile time lib major version in, server major version out
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>minor_in_out</parameter>
        </term>
        <listitem>
          <para>
            compile time lib minor version in, server minor version out
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>
          <parameter>reason_rtrn</parameter>
        </term>
        <listitem>
          <para>
            backfilled with a status code
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
    
    <para>
    <function>XkbOpenDisplay</function>
    is a convenience function that opens an X display connection and initializes
    the X keyboard extension. In all cases, upon return
    <parameter>reason_rtrn</parameter>
    contains a status value indicating success or the type of failure. If
    <parameter>major_in_out</parameter>
    and
    <parameter>minor_in_out</parameter>
    are not
    <symbol>NULL</symbol>,
    <function>XkbOpenDisplay</function>
    first calls
    <function>XkbLibraryVersion</function>
    to determine whether the client library is compatible, passing it the values
    pointed to by
    <parameter>major_in_out</parameter>
    and
    <parameter>minor_in_out</parameter>.
    If the library is incompatible,
    <function>XkbOpenDisplay</function>
    backfills
    <parameter>major_in_out</parameter>
    and
    <parameter>minor_in_out</parameter>
    with the major and minor extension versions of the library being used and
    returns
    <symbol>NULL</symbol>.
    If the library is compatible,
    <function>XkbOpenDisplay</function>
    next calls
    <function>XOpenDisplay</function>
    with the
    <parameter>display_name</parameter>.
    If this fails, the function returns
    <symbol>NULL</symbol>.
    If successful,
    <function>XkbOpenDisplay</function>
    calls
    <function>XkbQueryExtension</function>
    and
    backfills the major and minor Xkb server extension version numbers in
    <parameter>major_in_out</parameter>
    and
    <parameter>minor_in_out</parameter>.
    If the server extension version is not compatible with the library extension
    version or if the server extension is not present,
    <function>XkbOpenDisplay</function>
    closes the display and returns
    <symbol>NULL</symbol>.
    When successful, the function returns the display connection.
    </para>
    
    <para>
    The possible values for
    <parameter>reason_rtrn</parameter> are:
    </para>
    
    <itemizedlist>
    <listitem>
      <para>
    <errorname>XkbOD_BadLibraryVersion</errorname>
    indicates
    <function>XkbLibraryVersion</function>
    returned
    <symbol>False</symbol>.
      </para>
    </listitem>
    <listitem>
      <para>
    <errorname>XkbOD_ConnectionRefused</errorname>
    indicates the display could not be opened.
      </para>
    </listitem>
    <listitem>
      <para>
    <errorname>XkbOD_BadServerVersion</errorname>
    indicates the library and the server have incompatible extension versions.
      </para>
    </listitem>
    <listitem>
      <para>
    <errorname>XkbOD_NonXkbServer</errorname>
    indicates the extension is not present in the X server.
      </para>
    </listitem>
    <listitem>
      <para>
    <errorname>XkbOD_Success</errorname>
    indicates that the function succeeded.
      </para>
    </listitem>
    </itemizedlist>
    </sect1>
    
    <sect1 id='Disabling_the_Keyboard_Extension'>
    <title>Disabling the Keyboard Extension</title>
    <para>
    If a server supports the Xkb extension, the X library normally implements
    preXkb keyboard functions using the Xkb keyboard description and state. The
    server Xkb keyboard state may differ from the preXkb keyboard state. This
    difference does not affect most clients, but there are exceptions. To allow
    these clients to work properly, you may instruct the extension not to use Xkb
    functionality.
    </para>
    
    <para>
    Call
    <function>XkbIgnoreExtension</function>
    to prevent core X library keyboard functions from using the X Keyboard
    Extension. You must call
    <function>XkbIgnoreExtension</function>
    before you open a server connection; Xkb does not provide a way to enable or
    disable use of the extension once a connection is established.
    </para>
    
    <indexterm significance="preferred" zone="XkbIgnoreExtension"><primary><function>XkbIgnoreExtension</function></primary></indexterm>
    <funcsynopsis id="XkbIgnoreExtension">
      <funcprototype>
        <funcdef>Bool <function>XkbIgnoreExtension</function></funcdef>
    <!-- (
    <parameter>ignore</parameter>
    ) -->
    
        <paramdef>Bool <parameter>ignore</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
    <variablelist>
      <varlistentry>
        <term>
          <parameter>ignore</parameter>
        </term>
        <listitem>
          <para>
            <symbol>True</symbol> means ignore the extension
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
    
    <para>
    <function>XkbIgnoreExtension</function>
    tells the X library whether to use the X Keyboard Extension on any
    subsequently opened X display connections. If ignore is
    <symbol>True</symbol>,
    the library does not initialize the Xkb extension when it opens a new
    display. This forces the X server to use compatibility mode and communicate
    with the client using only core protocol requests and events. If ignore is
    <symbol>False</symbol>,
    the library treats subsequent calls to
    <function>XOpenDisplay</function>
    normally and uses Xkb extension requests, events, and state. Do not explicitly
    use Xkb on a connection for which it is disabled.
    <function>XkbIgnoreExtension</function>
    returns
    <symbol>False</symbol>
    if it was unable to apply the ignore request.
    </para>
    
    </sect1>
    <sect1 id='Protocol_Errors'>
    <title>Protocol Errors</title>
    <indexterm significance="preferred" zone="Protocol_Errors">
    <primary>errors</primary></indexterm>
    
    <para>
    Many of the Xkb extension library functions described in this document can
    cause the X server to report an error, referred to in this document as a
    <errorname>Bad<replaceable>Xxx</replaceable></errorname>
    protocol error, where
    <replaceable>Xxx</replaceable>
    is some name. These errors are fielded in the normal manner, by the default
    Xlib error handler or one replacing it. Note that X protocol errors are not
    necessarily reported immediately because of the buffering of X protocol
    requests in Xlib and the server.
    </para>
    
    <para>
    <link linkend="table2.1">Table 2.1</link>
    lists the protocol errors that can be generated, and their causes.
    </para>
    
    <table id='table2.1' frame='topbot'>
    <title>Xkb Protocol Errors</title>
    <?dbfo keep-together="always" ?>
    <tgroup cols='2' align='left' colsep='0' rowsep='0'>
    <colspec colname='c1' colwidth='1.0*'/>
    <colspec colname='c2' colwidth='3.0*'/>
    <thead>
      <row rowsep='1'>
        <entry>Error</entry>
        <entry>Cause</entry>
      </row>
    </thead>
    <tbody>
      <row>
        <entry><errorname>BadAccess</errorname></entry>
        <entry>
    <para>
    The Xkb extension has not been properly initialized
    </para>
        </entry>
      </row>
      <row>
        <entry><errorname>BadKeyboard</errorname></entry>
        <entry>
    <para>
    The device specified was not a valid core or input extension device
    </para>
        </entry>
      </row>
      <row>
        <entry><errorname>BadImplementation</errorname></entry>
        <entry>
    <para>
    Invalid reply from server
    </para>
        </entry>
      </row>
      <row>
        <entry><errorname>BadAlloc</errorname></entry>
        <entry>
    <para>
    Unable to allocate storage
    </para>
        </entry>
      </row>
      <row>
        <entry><errorname>BadMatch</errorname></entry>
        <entry>
    <para>
    A compatible version of Xkb was not available in the server or an argument has
    correct type and range, but is otherwise invalid
    </para>
        </entry>
      </row>
      <row>
        <entry><errorname>BadValue</errorname></entry>
        <entry>
    <para>
    An argument is out of range
    </para>
        </entry>
      </row>
      <row>
        <entry><errorname>BadAtom</errorname></entry>
        <entry>
    <para>
    A name is neither a valid Atom or
    <symbol>None</symbol>
    </para>
        </entry>
      </row>
      <row>
        <entry><errorname>BadDevice</errorname></entry>
        <entry>
    <para>
    Device, Feedback Class, or Feedback ID invalid
    </para>
        </entry>
      </row>
    </tbody>
    </tgroup>
    </table>
    
    <para id='BadKeyboard'>
    <indexterm zone="BadKeyboard"><primary>errors</primary>
    <secondary><errorname>BadKeyboard</errorname></secondary></indexterm>
    <indexterm zone="BadKeyboard">
    <primary><errorname>BadKeyboard</errorname></primary></indexterm>
    The Xkb extension adds a single protocol error,
    <errorname>BadKeyboard</errorname>,
    to the core protocol error set. This error code will be reported as the
    <parameter>error_rtrn</parameter>
    when
    <function>XkbQueryExtension</function>
    is called. When a
    <errorname>BadKeyboard</errorname>
    error is reported in an
    <structname>XErrorEvent</structname>,
    additional information is reported in the
    <structfield>resourceid</structfield>
    field. The most significant byte of the
    <structfield>resource_id</structfield>
    is a further refinement of the error cause, as defined in
    <link linkend="table2.2">Table 2.2</link>. The least
    significant byte will contain the device, class, or feedback ID as indicated in
    the table.
    </para>
    
    <table id='table2.2' frame='topbot'>
    <title><errorname>BadKeyboard</errorname> Protocol Error resource_id Values</title>
    <?dbfo keep-together="always" ?>
    <tgroup cols='4' align='left' colsep='0' rowsep='0'>
    <colspec colname='c1' colwidth='2.0*'/>
    <colspec colname='c2' colwidth='1.0*'/>
    <colspec colname='c3' colwidth='3.0*'/>
    <colspec colname='c4' colwidth='2.0*'/>
    <thead>
      <row rowsep='1'>
        <entry>high-order byte</entry>
        <entry>value</entry>
        <entry>meaning</entry>
        <entry>low-order byte</entry>
      </row>
    </thead>
    <tbody>
      <row>
        <entry><errorname>XkbErr_BadDevice</errorname></entry>
        <entry>0xff</entry>
        <entry>
    <para>
    device not found
    </para>
        </entry>
        <entry>device ID</entry>
      </row>
      <row>
        <entry><errorname>XkbErr_BadClass</errorname></entry>
        <entry>0xfe</entry>
        <entry>
    <para>
    device found, but it is of the wrong class
    </para>
        </entry>
        <entry>class ID</entry>
      </row>
      <row>
        <entry><errorname>XkbErr_BadId</errorname></entry>
        <entry>0xfd</entry>
        <entry>
    <para>
    device found, class ok, but device does not contain a feedback with the
    indicated ID
    </para>
        </entry>
        <entry>feedback ID</entry>
      </row>
    </tbody>
    </tgroup>
    </table>
    </sect1>
    
    <sect1 id='Display_and_Device_Specifications_in_Function_Calls'>
    <title>Display and Device Specifications in Function Calls</title>
    <para>
    Where a connection to the server is passed as an argument (Display*) and an
    <type>XkbDescPtr</type>
    is also passed as an argument, the Display* argument must match the
    <structfield>dpy</structfield>
    field of the
    <structname>XkbDescRec</structname>
    pointed to by the
    <type>XkbDescPtr</type>
    argument, or else the
    <structfield>dpy</structfield>
    field of the
    <structname>XkbDescRec</structname>
    must be
    <symbol>NULL</symbol>.
    If they don’t match or the
    <structfield>dpy</structfield>
    field is not
    <symbol>NULL</symbol>,
    a
    <errorname>BadMatch</errorname>
    error is returned (either in the return value or a backfilled
    <type>Status</type>
    variable). Upon successful return, the
    <structfield>dpy</structfield>
    field of the
    <structname>XkbDescRec</structname>
    always contains the Display* value passed in.
    </para>
    
    <para>
    The Xkb extension can communicate with the X input extension if it is present.
    Consequently, there can potentially be more than one input device connected to
    the server. Most Xkb library calls that require communicating with the server
    involve both a server connection (Display *
    <structfield>dpy</structfield>)
    and a device identifier (unsigned int
    <structfield>device_spec</structfield>).
    In some cases, the device identifier is implicit and is taken as the
    <structfield>device_spec</structfield>
    field of an
    <structname>XkbDescRec</structname>
    structure passed as an argument.
    </para>
    
    <para id='XkbUseCoreKbd'>
    <indexterm significance="preferred" zone="XkbUseCoreKbd"><primary><symbol>XkbUseCoreKbd</symbol></primary></indexterm>
    The device identifier can specify any X input extension device with a
    <symbol>KeyClass</symbol>
    component, or it can specify the constant,
    <symbol>XkbUseCoreKbd</symbol>.
    The use of
    <symbol>XkbUseCoreKbd</symbol>
    allows applications to indicate the core keyboard without having to determine
    its device identifier.
    </para>
    
    <para>
    Where an Xkb device identifier is passed as an argument and an
    <type>XkbDescPtr</type>
    is also passed as an argument, if either the argument or the
    <structname>XkbDescRec</structname>
    <structfield>device_spec</structfield>
    field is
    <symbol>XkbUseCoreKbd</symbol>,
    and if the function returns successfully, the
    <type>XkbDescPtr</type>
    <structfield>device_spec</structfield>
    field will have been converted from
    <symbol>XkbUseCoreKbd</symbol>
    to a real Xkb device ID. If the function does not complete successfully, the
    <structfield>device_spec</structfield>
    field remains unchanged. Subsequently, the device id argument must match the
    <structfield>device_spec</structfield>
    field of the
    <type>XkbDescPtr</type>
    argument. If they don’t match, a
    <errorname>BadMatch</errorname>
    error is returned (either in the return value or a backfilled
    <type>Status</type>
    variable).
    </para>
    
    <para>
    When the Xkb extension in the server hands an application a device identifier
    to use for the keyboard, that ID is the input extension identifier for the
    device if the server supports the X Input Extension. If the server does not
    support the input extension, the meaning of the identifier is undefined — the
    only guarantee is that when you use
    <symbol>XkbUseCoreKbd</symbol>,
    <symbol>XkbUseCoreKbd</symbol>
    will work and the identifier returned by the server will refer to the core
    keyboard device.
    </para>
    </sect1>
    </chapter>