Before each normal opening, clear the list, lock the public-screen list,
append each node name in enumeration order and unlock. Select the first
case-insensitive match with String_Contents. If no match exists, a
nonempty string selects Active_Off; an empty string requests entry zero.
Return success regardless of insertion failures. There is no live
refresh while the popup stays open.
An accepted deferred close sets String_Contents from the active entry if
one exists. It does not set String_Acknowledge. Double-click requests
Close(TRUE); cancellation does not copy a selection. Window and
queued-hook lifetimes follow Popobject/Popstring.