In some cases, the state implementation may want the checkbox to be "not changeable" from the State Editor. In this case,
the checkbox can be disabled using then setCheckboxEnabled(boolean).
The checkbox indicates whether the value entered in the "input field" should be treated as "<i>session variable name</i>"
when checked, or "<i>static value</i>" when not checked.
This method is used by the UI State Editor to enable/disable the UI checkbox component.