To truly allow for developers to create custom controls, we have to give them the full power of CSS. However, at present much of this API is exposed only via impl_* methods, which are @deprecated and therefore developers are strongly recommended against using. We need to determine whether this API is ready to be made public, and if so, make it public as part of the push to provide better custom controls API (see RT-21596).

Draft list of impl methods exposed/inherited in Controls code that we may wish to make public API:

     public static List<StyleableProperty> impl_CSS_STYLEABLES()
     public List<StyleableProperty> impl_getStyleableProperties()
     public long impl_getPseudoClassState()
     protected Boolean impl_cssGetFocusTraversableInitialValue()
     protected void impl_notifyLayoutBoundsChanged()
     public void impl_processCSS(boolean reapply)
     protected Bounds impl_computeLayoutBounds()
     protected Pos impl_cssGetAlignmentInitialValue()
     protected impl_pseudoClassStateChanged(String)