Since objects returned by Compiler methods are passed as arguments to other Compiler methods, the descriptions of these methods use virtual types. There are four virtual object types: EXPRESSION, QNAME, STEP and NODE_TEST.

The following example illustrates this notion. This sequence compiles the xpath "foo[round(1 div 2)]/text()":

      Object qname1 = compiler.qname(null, "foo")
      Object expr1 = compiler.number("1");
      Object expr2 = compiler.number("2");
      Object expr3 = compiler.div(expr1, expr2);
      Object expr4 = compiler.
              coreFunction(Compiler.FUNCTION_ROUND, new Object[]{expr3});
      Object test1 = compiler.nodeNameTest(qname1);
      Object step1 = compiler.
              step(Compiler.AXIS_CHILD, test1, new Object[]{expr4});
      Object test2 = compiler.nodeTypeTest(Compiler.NODE_TYPE_TEXT);
      Object step2 = compiler.nodeTypeTest(Compiler.AXIS_CHILD, test2, null);
      Object expr5 = compiler.locationPath(false, new Object[]{step1, step2});