Variables view: trimmable item

[Vladimir Prus]

Hello,
I have a question about internals of the 'TrimmableItem' class,
used a lot in variables view codes.

What is the purpose of the class? It looks that the idea is that when
stepping though the code, some local variables can go out of scope. In that
case, they will be "trimmed".

However, when stepping though the code the "info locals" command is issued at 
each step. So, why don't we simply clean all items, and repopulate the view,
instead of "trimming"?

TIA,
Volodya