code: public boolean matchesFunction() {
          if (remainingLength() < 3) {
              return false;
          }
          char first = peek();
          if (!Character.isLetter(first) && first != '_') {
              return false;
          }
  
          int start = pos + 1;
          for (; start < queue.length(); start++) {// xpath的函数名称里面,允许有 "-"
              if (Character.isLetterOrDigit(queue.charAt(start)) || queue.charAt(start) == '-') {
                  continue;
              }
              return queue.charAt(start) == '(' && queue.indexOf(')', start) > 0;
          }
          return false;
      }
docs: 测试是否是函数 abc() , //
  
  @return 是否是函数