in src/ext/guac.py [0:0]
def endpoint(option_value):
"""
Parses the given string, validating it against the set of valid endpoint
identifier strings ("client" or "server").
:param option_value:
The string to parse, as may be received from Sphinx as the value of a
directive option.
:return string:
The provided, valid string.
:raises ValueError:
If the provided endpoint is invalid.
"""
return directives.choice(option_value, ('client', 'server'))