How to import another projects' templates?

Yello~
learning GTK, love this tool!
Can't really find any resources on splitting up a project into multiple files. I found that it's not really made for that, and I'm fine with that, but it'd be nice if I could somehow at least import the file from another project if not edit it.
An example for this would be sick.
There is the custom widget example in the library, but it imports from "workbench.template", no clue what I should put there.
From what I understand atm (prolly wrong), I need to import the gresource from the other project, and then maybe put that into the Template field of registerClass?

Thanks for any tips~

Start with the library's custom widget example and its “workbench.template” import, then trace how templates and the registerClass Template field are handled. Document whether importing a template from another project is supported and provide a working example, including the required resource setup. Done when a newcomer can follow the example without guessing what to put in the import or Template field.