u'''Insert a tab character.

def tab_insert(self, e):  # (M-TAB)
        u'''Insert a tab character. '''
        cursor = min(self.l_buffer.point, len(self.l_buffer.line_buffer))
        ws = ' ' * (self.tabstop - (cursor % self.tabstop))
        self.insert_text(ws)
        self.finalize()