This is an interesting question: How to deselect all? I thought I knew the answer, but then tried it and... I didn't, but now I know the answer.
You may or may not know that control-a does select all. The sister command, shift-control-a is what I thought did a deselect. But it doesn't! Shift-control-a INVERTS the selection. That's not terribly useful for me, but I can see why you would want it.
So how do you deselect all? It's not a menu item. It's not a keyboard shortcut (according to the docs). Impossible? Well.. almost. I found the MCC command for deselect all (MCC 21015). Then mapped it to a custom keyboard shortcut using the Resource.xml file. Here's the relevant part from my file:
<!-- Deselect all -->
<Entry Key="Ctrl;Shift;a" Command="21015" />
Now the shift-control-a (which is not useful to me as invert selection) does deselect all!
If you don't want to go through the (moderate) hassle of setting up the Resource.xml file and putting this in it, I have a different sequence of keys that will work for you:
1. control-a : This will select all
2. shift-control-a. : Now that all is selected, the "invert selection" key will select none.
Effectively this is a deselect all. It's just two different keyboard shortcuts to get there.
I prefer my way, but then again it's "my way." lol
Have fun.
Brian.