Nancy, it's OK as far as it goes.
Most of what it covers does not need Web Blocks.

I've found their main benefit is to shuffle things around.
When you want to be creative, they are a drag.

The art of hiding all the Paste > Unformatted Text into the defaults blocks is pure artifice.
Factoring that part back in and you are into hours.

It didn't show that when you add something into a Main WB, it doesn't appear in the Variant so you can be back and forth.
It makes no mention of the lock-in Xara has imposed with its Layout grouping that you cannot edit into. It is easy to destroy a WB's functionality and not realise immediately.
Try opening a WB that has Embedded Graphics/Groups.

You cannot place WBs adjacent to one another so you have a highly constrained design.

Interesting that NavBars are not a WB.

Acorn