This function starts helpviewer, if necessary, and displays the page corresponding to the specified URL address.
Gamma> PxHelpUrl("/usr/help/product/gamma/photon/PtBarGraph.html");
t <The PtBarGraph helpviewer page is displayed.>
PxHelpQuit, PxHelpTopic, PxHelpTopicRoot, PxHelpTopicTree, PxHelpUrlRoot
and in Photon documentation: PxHelpUrl.