XQueryExtension, XListExtensions, XFreeExtensionList - list available extensions
Bool XQueryExtension(display, name,
    major_opcode_return, first_event_return,
    first_error_return)
char **XListExtensions(display,
    nextensions_return)
XFreeExtensionList(list)
  - display
- Specifies the connection to the X server.
- name
- Specifies the extension name.
- major_opcode_return
- Returns the major opcode.
- first_event_return
- Returns the first event code, if any.
- first_error_return
- Returns the first error code, if any.
- nextensions_return
- Returns the number of extensions listed.
- list
- Specifies the list of extension names.
The XQueryExtension function determines if the named extension is
  present. If the extension is not present, XQueryExtension returns
  False; otherwise, it returns True. If the extension is present,
  XQueryExtension returns the major opcode for the extension to
  major_opcode_return; otherwise, it returns zero. Any minor opcode and the
  request formats are specific to the extension. If the extension involves
  additional event types, XQueryExtension returns the base event type
  code to first_event_return; otherwise, it returns zero. The format of the
  events is specific to the extension. If the extension involves additional
  error codes, XQueryExtension returns the base error code to
  first_error_return; otherwise, it returns zero. The format of additional data
  in the errors is specific to the extension. If the extension name is not in
  the Host Portable Character Encoding the result is implementation-dependent.
  Uppercase and lowercase matter; the strings “thing”,
  “Thing”, and “thinG” are all considered different
  names.The XListExtensions function returns a list of all
    extensions supported by the server. If the data returned by the server is in
    the Latin Portable Character Encoding, then the returned strings are in the
    Host Portable Character Encoding. Otherwise, the result is
    implementation-dependent.
The XFreeExtensionList function frees the memory allocated
    by XListExtensions.