How to show 'tabs' and 'whitespaces' in diff viewer

Hi All

How to activate/show 'tabs' and 'whitespaces' within the diff viewer?

As a complete newby I'm today 'playing' with Collaborator. I'm used to Beyond Compare and I already found how to couple this tool. However within Beyond Compare I cannot add comments so I want to use the internal 'diff viewer' instead. But how can I enable the view to show the 'tabs' and 'whitespaces'? Within my current view I can only see a difference, but not what is used (we have some mandatory formatting rules). So how to activate this?

Thanks

Ludo