Scrolling List selected lines

[Peter Haworth]

I'm trying to find a message that is sent when I click on a line in a
scrolling list field that happens before the selectedline property changes
to show the line that was just clicked.

I've tried mouseDown and selectionChanged but the selectedLines property
has already changed when I get them.

The purpose is to remember the selectedLines before the most recent click.
I can do it by storing the selected lines in a script local variable but
just curious to know if there is a message that is sent before the
selectedLines property changes.