Show block content only to certain roles

I've modified the handbook entry 'Show block content only to certain roles' (http://drupal.org/node/27690) slightly. Of course I looked at the comments and used their content to (I hope) improve the entry. This means that current comments can be removed.

Log:

Rewrote the examples (because of comments):
- made example 1 safer (is_array)
- rewrote & expanded example 2, to clearly include multiple roles
- added negation
- expanded foo to "content goes here"

Please review the page and comment.