xpaxt - Man Page
XPAXt: the XPA Interface to Xt (X Windows)
Describes how XPA access points can be added to X Toolkit (Xt) programs.
XPA supports Xt programs: you can call XPANew(), XPACmdNew(), or XPAInfoNew() within any C routine to add XPA server callbacks to an Xt program. Since an Xt program has its own event loop call (i.e., XtAppMainLoop()), it therefore does not need or want to use the XPA even loop. Thus, in order to add XPA access points to the standard Xt event loop, the following routine should be called before entering the loop:
int XPAXtAddInput(XtAppContext app, XPA xpa)
The XPAAddAddInput() routine will add XPA access points to the Xt event loop by making calls to the standard XtAppAddInput() routine. (If the XtAppContext argument is NULL, then the alternate XtAddInput() routine is used instead.) If the xpa argument is NULL, then all active XPA access points are added to the loop. If xpa is not NULL, then only the specified access point is added. The latter type of call is used to add new access points from within a callback, after the program has entered the XtAppMainLoop() even loop.
See xpa(n) for a list of XPA help pages