@classmethod<EOL><INDENT>def get_as_var(cls, tokens):<DEDENT>
as_var = None<EOL>if tokens[-<NUM_LIT:2>] == '<STR_LIT>':<EOL><INDENT>as_var = tokens[-<NUM_LIT:1>]<EOL>tokens[-<NUM_LIT:2>:] = []<EOL><DEDENT>return as_var<EOL>
Returns context variable from `as` template tag clause if any.

         Modifies tokens inplace.

        :param tokens:
        :rtype: None|str