def render(self, ctx=None):
        '''
        Render only the mutated field (or the first one if not in mutation)

        :param ctx: rendering context in which the method was called
        :rtype: `Bits`
        :return: rendered value of the container
        '''
        if ctx is None:
            ctx = RenderContext()
        ctx.push(self)
        self._initialize()
        offset = self.offset if self.offset else 0
        self._fields[self._field_idx].set_offset(offset)
        rendered = self._fields[self._field_idx].render(ctx)
        self.set_current_value(rendered)
        ctx.pop()
        return self._current_rendered
Render only the mutated field (or the first one if not in mutation)

        :param ctx: rendering context in which the method was called
        :rtype: `Bits`
        :return: rendered value of the container