\csname

yex.keyword.Csname(parser)

Creates new control tokens.

\csname must be followed by a series of tokens of any of the basic categories. Expandable controls will be expanded; unexpandable controls aren't allowed. The series must end with \endcsname.

This series will become the name of a new control token, which will initially point at \relax. See p40 of the TeΧbook for more details.

You can use this to create control tokens with weird names-- even the empty string. Note that if you create a token with a name beginning with an underscore, that underscore will be doubled in doc[name] so that it doesn't conflict with yex's internal settings.

Source code in yex/keyword/other.py

@yex.decorator.control()
def Csname(parser):
    r"""
    Creates new control tokens.

    \csname must be followed by a series of tokens of any of the basic
    categories. Expandable controls will be expanded; unexpandable controls
    aren't allowed. The series must end with \endcsname.

    This series will become the name of a new control token, which will
    initially point at \relax. See p40 of the TeXbook for more details.

    You can use this to create control tokens with weird names-- even
    the empty string. Note that if you create a token with a name
    beginning with an underscore, that underscore will
    be doubled in doc[name] so that it doesn't conflict with yex's internal
    settings.
    """

    logger.debug(r'\csname: reading name of new control')

    location = parser.location

    name = ''
    try:
        while True:
            item = parser.next(level='executing', on_eof='raise')

            if isinstance(item, yex.parse.Token) and item.is_from_tex:
                name += item.ch
            else:
                raise yex.exception.CsnameWeirdFollowingError(
                        problem = item,
                        )
    except yex.exception.EndcsnameError:
        pass

    if name.startswith('_'):
        name = f'_{name}'

    logger.debug(r'\csname: new control will be called %s', name)

    result = yex.parse.ControlName(
            ch = name,
            location = location,
            )

    logger.debug(r'\csname: new control is %s', result)

    name_with_backslash = '\\'+name
    if name_with_backslash not in parser.doc.controls:
        parser.doc.controls[name_with_backslash] = Relax()
        logger.debug(r'\csname: added to controls table')

    return result