Querying textfield

Hi all,
I am building an external that makes use of a textfield.
I see from the ui_textfield example that you can query the size and text of said textfield, but can find no way of ascertaining whether all or part of the text is currently selected/highlighted (by double clicking to select all, typing Command A, or click dragging to select part thereof).
If anyone could clarify if there is a method which can be called I would be most thankful.
Kind regards,
Leigh