The difference between Drupal 5 and 6. Slightly outdated.

Notice that most of PHPTemplate engine has been moved deeper into the core theme() function. This allows modules and core .inc files to default it's output to .tpl files. This means themers do not have to manually setup a callback function.

A good handful of functions in core has already been converted. This means less to do for themers. Duplicating the files into the theme will let themers override the output. Easy!

PDF's attached to this node.

Documentation forthcoming in the new theming handbook.