Template suggestion for 'content' in custom page I need the equivalent for hook_preprocess_node for custom pages, which aren't nodes.

The particular page I need to theme is provided by the entity registration module 'node/10/register'. I can add theme suggestions for the page using hook_preprocess_page - but how to I add a theme suggestion for the actual content, so I don't have to rewrite the page.tpl.php? 

Alternatively if there is an existing pattern to name the file then that would be even better.
You need to copy the file

entity.tpl.php 


from the theme directory of the module : entity.

Paste it into your theme's template directory, and rename it to 

registration.tpl.php


Other theme suggestions are:

registration__TYPE
registration__TYPE__VIEWMODE
registration__ID


If you want to have access to the preprocess function then add this function to your theme's template.php file :

function MYTHEME_preprocess_entity(&amp;$vars) {
  //dpm($vars);
}