 that includes functions
    that are known to php but are undocumented.

    To get a list of allowed modules have a look into the
    `_php_builtins` module:

    .. sourcecode:: pycon

        >>> from pygments.lexers._php_builtins import MODULES
        >>> MODULES.keys()
        ['PHP Options/Info', 'Zip', 'dba', ...]

    In fact the names of those modules match the module names from
    the php documentation.
