Writing custom controls in JavaFX is a simple and straight forward process. A control class is needed for controlling the state of the control (hence the name). A skin class is needed for the apperance of the control. And more often than not a CSS file for customizing the apperance.
A common approach for controls is to hide the nodes they are using inside their skin class. The TextField control for example uses two instances of javafx.scene.text.Text. One for the regular text, one for the prompt text. These nodes are not accessible via the TextField API. If you want to get a reference to them you would need to call the lookup(String) method on Node. So far so good. It is actually hard to think of use cases where you would actually need access to the Text nodes.
It becomes a whole different story if you develop complex custom controls. The FlexGanttFX Gantt charting framework is one example. The GanttChart control consists