Just some questions #23

I have two questions:

1. How are conditional comments compared?

I get some differences about comments and I do not understand it.

Lets say you have a comment like this:

Is it one big comment or 2 comments and 1 node?

<!--[if mso | IE]>
<table />
<![endif]-->

If it is 2 comments and 1 node, how are whitespaces handled?

2. Can I ignore some attributes? I would like to ignore empty style attributes like style=""