Theme Hook Suggestions
The default implementation of template files and theme functions offer a very generic set of markup that is sufficient, but not ideal in all cases. When doing a standard override, such as copying
block.tpl.php into a theme, the changes made will apply site-wide whenever a block is rendered. At times this the desired result, but you’ll often want to make changes to a specific block, a set of blocks provided by a specific module, or even a group of blocks in a specific region.
Theme hook suggestions allow you to implement targeted overrides in your theme for both template files and theme functions with naming patterns. The options and naming patterns vary depending on what type of object you are working with. During the preprocess stage, before each template is rendered, a variable called
$theme_hook_suggestions is created and populated with alternative hook suggestions.