XtReservePropertyAtom, XtReleasePropertyAtom - maintain a cache of property
  atoms
#include <X11/Intrinsic.h>
Atom XtReservePropertyAtom(Widget w);
void XtReleasePropertyAtom(Widget w, Atom
  atom);
  - w
- Specifies the widget used to reserve the atom.
- atom
- Specifies the atom whose reservation is to be released.
XtReservePropertyAtom returns an atom that may be used for properties in
  conjunction with conversion requests from widget w. The atom returned
  will be unique for the display of the widget specified.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface