There is currently no way to find out exactly how much visible space is available to those children of a Parent that are added by the client. This is mostly an issue for parents that show scroll bars (possibly dynamically), e.g. when attempting to automatically size the columns of a TableView. Visible client space may be reduced by the scroll bar size, and there is no public API to discover by how much. Digging through the private implementation details of the currently loaded skin is not a good solution.

Ideally, Parent should have read-only properties getClientWidth/Height that return the Parent's size minus whatever non-client decoration and private children (such as scrollbars) the Parent is currently showing. At a minimum, any Parent with scroll bars should expose their width (for vertical scroll bars) and height (for horizontal scroll bars), as well as flags to indicate which are being shown at the moment.