#PB_Tree_Unchecked missing

[PB]

There's #PB_Checkbox_Unchecked for turning off a CheckBox, but
there's no #PB_Tree_Unchecked for checkboxes in a TreeGadget.

Or is it expected that we use #PB_Checkbox_Unchecked for it?
The manual doesn't say that we can; it only shows how to check:

#PB_Tree_Checked : The items checkbox should be checked.

Something like this should be there, IMO:

#PB_Tree_Checked : The items checkbox should be checked.
#PB_Tree_Unchecked : The items checkbox should be unchecked.