drupal version is 6. just want to know where are those $body_classes comes form.

I knew in template_preprocess_page , there is a variable called 'body_classes'.

but my problem is, not all body_classes are come from preprocess page.

for instance:

I have a term named 'activities and attractions', then in my page.tpl.php, there is a class 'page-activities and attractions' in my tag. looks like taxonomy module generates a body_class, but i could find it after search seource code of taxonomy module.