code: private Ref plusMinusOp() throws PageException {
  	Ref ref = modOp();
  
  	while (!cfml.isLast()) {
  	    // Plus Operation
  	    if (cfml.forwardIfCurrent('+')) {
  		ref = _plus(ref);
  	    }
  	    // Minus Operation
  	    else if (cfml.forwardIfCurrent('-')) {
  		ref = _minus(ref);
  	    }
  	    else break;
  	}
  	return ref;
      }
docs: Transfomiert die mathematischen Operatoren Plus und Minus (1,-). <br />
  EBNF:<br />
  <code>modOp [("-"|"+") spaces plusMinusOp];</code>
  
  @return CFXD Element
  @throws PageException