def first_simple_sel(rule)
      sseq = first_sseq(rule)
      return unless sseq.is_a?(Sass::Selector::SimpleSequence)
      sseq.members.first
    end
def first_simple_sel(rule)
      sseq = first_sseq(rule)
      return unless sseq.is_a?(Sass::Selector::SimpleSequence)
      sseq.members.first
    end
Return the first {Sass::Selector::Simple} in a {Sass::Tree::RuleNode},
 unless the rule begins with a combinator.

 @param rule [Sass::Tree::RuleNode]
 @return [Sass::Selector::Simple?]