docs: Expression XreadBooleanPredicand() {
  
          Expression e;
  
          if (token.tokenType == Tokens.OPENBRACKET) {
              read();
  
              e = XreadBooleanValueExpression();
  
              readThis(Tokens.CLOSEBRACKET);
  
              return e;
          } else {
              return XreadSimpleValueExpressionPrimary();
          }
      }