@rule('<STR_LIT>')<EOL><INDENT>def visit_slice_content(self, _, children):<DEDENT>
return children[<NUM_LIT:0>]<EOL>
The content of a slice (to be in brackets)

        Arguments
        ---------
        _ (node) : parsimonious.nodes.Node.
        children : list
            - 0: slice or number

        Returns
        -------
        slice or number
            The slice or number got from ``children[1]``

        Example
        -------

        >>> SliceParserMixin('1', default_rule='SLICE_CONTENT').data
        1
        >>> SliceParserMixin(':', default_rule='SLICE_CONTENT').data
        slice(None, None, None)
        >>> SliceParserMixin('1:', default_rule='SLICE_CONTENT').data
        slice(1, None, None)
        >>> SliceParserMixin('1:2:3', default_rule='SLICE_CONTENT').data
        slice(1, 2, 3)