I readed a tutorial about this matter in XOOPS and start working for use that feature in ImpressCMS. Module templates are applied for all module contents, but using templates in the editor you can predefinied a HTML design for certain content types in a module. For example: a special design accordin each product type or whatever you want. Flexibility is great.
1.- Option: If you use the great TinyConfig module, just add the word template in plugins and theme advanced buttons.
If not you must edit the file /editors/tinymce/tinymce.php.
Just around line 93
and in line 104
add ,template and save the file. Now you have a new button the editor.
2.- You need load the external template files.
About line 231 just after force_br_newlines add:
The content for that file will be:
3.- Create your template files (they must to be in html format, but without html, body or head tags, the root folder and submit liste.js file.
More info about this matter.