Partially supported system functions

• IsNull � the IsNull function is supported for simple datatypes only. It is not very useful for structure and class objects, since in .NET targets, uninitialized variables always return true for an IsNull call even when they are not explicitly set to null. However, you can use IsValid to test for valid instances of these object types. You can also use IsNull for class objects after they have been created.
• Timer � the concept of “current window” does not exist in Web Forms applications. Therefore, you must use the optional PowerScript syntax with the window name parameter and the name of an active window as the parameter value. The Timer function fails when the active window does not exist.
• Yield � due to the thread-model design of Web Forms applications, you cannot use the Yield function and the Selected event of a menu object concurrently. Doing this causes a JavaScript error.
• Registry functions � system registry functions can read and write registry entries, keys, and values on the server side, but do not perform these operations on the server computer�s registry in the same way as they do on a client computer�s registry in a standard PowerBuilder application. See Registry Functions for Web Forms Applications
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