Idea Summary
“Master pages”, behaving like a global page, except that it could be linked to selected pages. 

Currently, this can be done using conditionals on page 0, but
-all these conditionals must be executed when each page loads
- it greatly obscures the logic placed on page 0

Use Case
I often have regions that are the same for many pages. In order not to copy between pages, page 0 works very well for this purpose. But when I have more such regions, e.g. I want one region on a certain type of page, another on a different type of page, then suddenly page zero can have a lot of logic embedded in it, which is difficult to maintain.

Preferred Solution
In addition to page 0, which is still global to the entire application, I can create a "master" page that has exactly the same restrictions as page 0, but I can attach it to selected pages.

Then, when rendering, it loads the elements of page 0 + the elements of the attached master pages + the elements of the given page.