I found a rather interesting essay on the Harry Potter Wiki, written by the user Acrobasis01, which in my opinion is well-researched enough to be canon. Read for yourself:
Rowling gives enough information in Goblet of Fire and in a statement to fans at a reading at a cancer care center in Glasgow to locate Durmstrang in a specific country and possibly in a specific region of that country. She gives 10 very specific clues.
1. In the "far north." (Rowling 2000, 23:417)
2. Access to the sea. (Rowling 2000, 15:246)
3. Must predate 1294. (Rowling 2000, 12:187)
4. Castle has only "four floors". (Rowling 2000, 23:417)
5. Few hours of daylight in winter. (Rowling 2000, 23:417)
6. Extensive grounds. (Rowling 2000, 23:417)
7. Mountains. (Rowling 2000, 23:417) …Read more >
This is way too long of an essay to include as a reference on the appropriate page, so here goes. For those who somehow don't know, we're discussing here how we know Dolores Umbridge is pure-blood.
Well, we actually don't know anything - J. K. Rowling often surprises us with this sort of thing. But we've got a lot more evidence for this than for other things stated on here.
First and foremost: the truly, irrefutably canon bit: the WOMBAT Test from J. K. Rowling's Official Site, archived at the Harry Potter Wiki at the link given, states that all Wizengamot members must provide evidence of pure-blood status. Umbridge was on the Wizengamot as of 1995, and therefore had to have shown pure-blood credentials.
We know she was either half-blood or pure-blood,…Read more >