Required regions for a theme Are there a set of required regions for a theme that they must have?

I thought I read this in the documentation at one point, but I can't find it again.
The required regions:

regions[content] = Content
regions[help] = Help
regions[page_top] = Page top
regions[page_bottom] = Page bottom


More on this can be found at http://drupal.org/update/themes/6/7#closure