class Sass::Tree::ExtendNode

def cssize(extends, parent)
  @resolved_selector.members.each do |seq|
    if seq.members.size > 1
      raise Sass::SyntaxError.new("Can't extend #{seq.to_a.join}: can't extend nested selectors")
    end
    sseq = seq.members.first
    if !sseq.is_a?(Sass::Selector::SimpleSequence)
      raise Sass::SyntaxError.new("Can't extend #{seq.to_a.join}: invalid selector")
    end
    sel = sseq.members
    parent.resolved_rules.members.each do |seq|
      if !seq.members.last.is_a?(Sass::Selector::SimpleSequence)
        raise Sass::SyntaxError.new("#{seq} can't extend: invalid selector")
      end
      extends[sel] = seq
    end
  end
  []
end