code: function mostSpecific(instructions) {
      instructions = instructions.filter(function (instruction) { return isPresent(instruction); });
      if (instructions.length == 0) {
          return null;
      }
      if (instructions.length == 1) {
          return instructions[0];
      }
      var first = instructions[0];
      var rest = instructions.slice(1);
      return rest.reduce(function (instruction, contender) {
          if (compareSpecificityStrings(contender.specificity, instruction.specificity) == -1) {
              return contender;
          }
          return instruction;
      }, first);
  }
docs: /*
  Given a list of instructions, returns the most specific instruction