rmatting
        sequence currently being parsed, the buffer is used as the content for
        L{_attrs} before being added to L{_result} and emptied upon calling
        L{emit}.

    @type _attrs: C{set}
    @ivar _attrs: Set of the applicable formatting states (bold, underline,
        etc.) for the current L{_buffer}, these are applied to L{_buffer} when
        calling L{emit}.

    @type foreground: L{_ForegroundColorAttr}
    @ivar foreground: Current foreground color attribute, or L{None}.

    @type background: L{_BackgroundColorAttr}
    @ivar background: Current background color attribute, or L{None}.

    @ivar _result: Current parse result.
    Ú