Theme Developer module

This module which is part of the Devel module in Drupal 6, makes theming a great deal easier. It makes it quick to find out what selector in what stylesheet, or what .tpl file, or what function, is controlling the output - so that you can make changes directly.

Enable the block, and you will see a grey box, 'Themer Info', in the bottom left of your screen. Click on it to enable the Theme Developer tool which allows you to click on any element on your page and see information about what is outputting it.

For a .tpl file, you will see a list of variables available to you. If you click on the filename in the 'File used' line, you can quickly see the actual code in the file.

You need to clear the cache to see theme changes if you add a new file. The Devel module block, which has to be enabled in Site buidling >> Blocks, has a link to clear cache quickly.

For functions, function arguments are listed. You can also click on the function name to go to the API documentation at drupal.org. You can now create a .tpl file to take over the theming role of the function - see 'Converting from functions to templates' near the bottom of http://drupal.org/node/173880.

Disable Theme Developer when not needed because of <span> tags.