code: private Operation parseUrlParam() {
          StringBuilder builder = cachesBuilder;
          builder.setLength( 0 );
          Operation op = new Operation( reader, new ValueExpression( reader, relativeURL.getPath() ), ';' );
          for( ;; ) {
              char ch = read();
              switch( ch ) {
                  case '"':
                  case '\'':
                      String val = builder.toString();
                      String quote = readQuote( ch );
                      builder.append( val );
                      builder.append( quote );
                      break;
                  case '\\': //escape
                      builder.append( ch );
                      builder.append( read() );
                      break;
                  case '@':
                      if( builder.length() == 0 ) {
                          reader.back( ch );
                          op.addOperand( parseExpression( (char)0 ) );
                          read();
                          return op;
                      }
                      builder.append( ch );
                      break;
                  case ')':
                      val = trim( builder );
                      op.addOperand( new ValueExpression( reader, val, Expression.STRING ) );
                      return op;
                  default:
                      builder.append( ch );
              }
          }
      }
docs: Parse the parameter of an "url" function which has some curious fallbacks.
  
  @return the parameter of the function