code: public String scanFilterArgument() {
          if (end()) {
              return null;
          }
  
          int cp = string.codePointAt(pos);
          if (!Character.isJavaIdentifierStart(cp)) {
              return null;
          }
  
          int begin = pos;
          pos += Character.charCount(cp);
  
          for (; pos < string.length(); pos += Character.charCount(cp)) {
              cp = string.codePointAt(pos);
              if (!Character.isJavaIdentifierPart(cp) && cp != '.' && cp != '-') {
                  break;
              }
          }
  
          return string.substring(begin, pos);
      }
docs: Scan an argument to the ${servicePidOrFilter()} expression.
  
  @return