Man page 3 : XkbFindOverlayForKey

XkbFindOverlayForKey - Find the alternate name by using the primary name for a key that is part of an overlay

char * XkbFindOverlayForKey (XkbGeometryPtr geom , XkbSectionPtr section , char * under );

• - geom
      geometry that contains the section
• - section
      section to be searched for matching keys
• - under
      primary name of the key to be considered

Keys that can generate multiple keycodes may be associated with multiple names. Such keys have a primary name and an alternate name. XkbFindOverlayForKeyuses the primary name of the key, under,to look up the alternate name, which it returns.