I've some problem with themes and preprocess functions.
I see that, if I declare a variable in, for example, MYTHEME_preprocess_region(&$vars), this variable is available ONLY in region.tpl.php (I'm using Omega). But in preprocess_region and region.tpl there is the $vars['node'] variable (if I'm displaying a node), so in these functions I can't create variable based on $node.
In my example, the $vars['node'] variable is available in preprocess_page and preprocess_node.
The question is: if I want to add on region.tpl.php (or preprocess_region) a variable based on $node how should I do?
The "general" question is: how can I declare a variable in a theme function, in template.php, and let this function available in other functions?