XtCreateWidget, XtVaCreateWidget, XtCreateManagedWidget,
  XtVaCreateManagedWidget, XtDestroyWidget - create and destroy widgets
#include <X11/Intrinsic.h>
Widget XtCreateWidget(const char *name, WidgetClass
    widget_class, Widget parent, ArgList args, Cardinal
    num_args);
Widget XtVaCreateWidget(const char *name, WidgetClass
    widget_class, Widget parent, ...);
Widget XtCreateManagedWidget(const char *name,
    WidgetClass widget_class, Widget parent, ArgList args,
    Cardinal num_args);
Widget XtVaCreateManagedWidget(const char *name,
    WidgetClass widget_class, Widget parent, ...);
void XtDestroyWidget(Widget w);
  - args
- Specifies the argument list to override the resource defaults.
- name
- Specifies the resource name for the created widget, which is used for
      retrieving resources and, for that reason, should not be the same as any
      other widget that is a child of same parent.
- num_args
- Specifies the number of arguments in the argument list.
- parent
- Specifies the parent widget.
- w
- Specifies the widget.
- widget_class
- Specifies the widget class pointer for the created widget.
- ...
- Specifies the variable argument list to override the resource
    defaults.
The XtCreateWidget function performs much of the boilerplate operations
  of widget creation:
  - Checks to see if the class_initialize procedure has been called for this
      class and for all superclasses and, if not, calls those necessary in a
      superclass-to-subclass order.
- Allocates memory for the widget instance.
- If the parent is a subclass of constraintWidgetClass, it allocates
      memory for the parent's constraints and stores the address of this memory
      into the constraints field.
- Initializes the core nonresource data fields (for example, parent and
      visible).
- Initializes the resource fields (for example, background_pixel) by using
      the resource lists specified for this class and all superclasses.
- If the parent is a subclass of constraintWidgetClass, it
      initializes the resource fields of the constraints record by using the
      constraint resource list specified for the parent's class and all
      superclasses up to constraintWidgetClass.
- Calls the initialize procedures for the widget by starting at the
      Core initialize procedure on down to the widget's initialize
      procedure.
- If the parent is a subclass of compositeWidgetClass, it puts the
      widget into its parent's children list by calling its parent's
      insert_child procedure. For further information, see Section 3.5.
- If the parent is a subclass of constraintWidgetClass, it calls the
      constraint initialize procedures, starting at constraintWidgetClass
      on down to the parent's constraint initialize procedure.
Note that you can determine the number of arguments in an argument
    list by using the XtNumber macro. For further information, see
    Section 11.1.
The XtCreateManagedWidget function is a convenience routine
    that calls XtCreateWidget and XtManageChild.
The XtDestroyWidget function provides the only method of
    destroying a widget, including widgets that need to destroy themselves. It
    can be called at any time, including from an application callback routine of
    the widget being destroyed. This requires a two-phase destroy process in
    order to avoid dangling references to destroyed widgets.
In phase one, XtDestroyWidget performs the following:
  - If the being_destroyed field of the widget is True, it returns
      immediately.
- Recursively descends the widget tree and sets the being_destroyed field to
      True for the widget and all children.
- Adds the widget to a list of widgets (the destroy list) that should be
      destroyed when it is safe to do so.
Entries on the destroy list satisfy the invariant that if w2
    occurs after w1 on the destroy list then w2 is not a descendent of w1. (A
    descendant refers to both normal and pop-up children.)
Phase two occurs when all procedures that should execute as a
    result of the current event have been called (including all procedures
    registered with the event and translation managers), that is, when the
    current invocation of XtDispatchEvent is about to return or
    immediately if not in XtDispatchEvent.
In phase two, XtDestroyWidget performs the following on
    each entry in the destroy list:
  - Calls the destroy callback procedures registered on the widget (and all
      descendants) in post-order (it calls children callbacks before parent
      callbacks).
- If the widget's parent is a subclass of compositeWidgetClass and if
      the parent is not being destroyed, it calls XtUnmanageChild on the
      widget and then calls the widget's parent's delete_child procedure (see
      Section 3.4).
- If the widget's parent is a subclass of constraintWidgetClass, it
      calls the constraint destroy procedure for the parent, then the parent's
      superclass, until finally it calls the constraint destroy procedure for
      constraintWidgetClass.
- Calls the destroy methods for the widget (and all descendants) in
      post-order. For each such widget, it calls the destroy procedure declared
      in the widget class, then the destroy procedure declared in its
      superclass, until finally it calls the destroy procedure declared in the
      Core class record.
- Calls XDestroyWindow if the widget is realized (that is, has an X
      window). The server recursively destroys all descendant windows.
- Recursively descends the tree and deallocates all pop-up widgets,
      constraint records, callback lists and, if the widget is a subclass of
      compositeWidgetClass, children.
XtAppCreateShell(3), XtCreatePopupShell(3)
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface