accept

# File lib/optparse.rb, line 537
    def accept(t, pat = /.*/, &block)
      if pat
        pat.respond_to?(:match) or
          raise TypeError, "has no `match'", ParseError.filter_backtrace(caller(2))
      else
        pat = t if t.respond_to?(:match)
      end
      unless block
        block = pat.method(:convert).to_proc if pat.respond_to?(:convert)
      end
      @atype[t] = [pat, block]
    end