def tag(label)
      abort ArgumentError.new "Tag must be a String or Symbol" unless [String, Symbol].include?(label.class)
      @tags << label
    end
def tag(label)
      abort ArgumentError.new "Tag must be a String or Symbol" unless [String, Symbol].include?(label.class)
      @tags << label
    end
Tag a call with an arbitrary label

 @param [String, Symbol] label String or Symbol with which to tag this call