In X11R3:
  Resources that are inherited from a superclass cannot be set
  by functions like create-widget; they must be set after the
  widget has been created by a call to set-values! (this restricition
  only there for the first widget of each class)

Subresources cannot be read by means of get-values.

Callbacks *must* return; e.g. a (reset) from within a callback is
not allowed.  This is a bug in Xt.

Xt doesn't notice when ports that have been registered as input source
with context-add-input are closed.  In this case, the select() fails.

Missing:

  keycode translators
  case converters
  shared graphics contexts
  selections

  2.
  XtScreen
  XtDisplayOfObject
  XtScreenOfObject
  XtWindowOfObject

  7.
  XtGrabKey
  XtGrabKeyboard
  XtGrabButton
  XtGrabPointer
  XtSetKeyboardFocus
  XtCallAcceptFocus
  XtAppPeekEvent, XtAppNextEvent, XtDispatchEvent (?)
  Xt{Add,Remove,Insert}EventHandler (?)
  Xt{Add,Remove,Insert}RawEventHandler (?)
  XtBuildEventMask (?)

  9.
  XtGetSubresources (?)
  XtGetApplicationResources
  XtGetSubvalues, XtSetSubvalues (?)

  10.
  XtAppAddActions (?)
  XtAppAddActionHook (?)
  XtRemoveActionHook (?)
  XtParseAcceleratorTable (?)
  XtInstallAccelerators (?)
  XtInstallAllAccelerators (?)

  11.
  XtAppSetSelectionTimeout
  XtAppGetSelectionTimeout
  XtAppSetWarningMsgHandler
  XtSetWMColormapWindows
