level requirement of upgraded items

[adeyke]

So the +5/+7/+12 applies not only to unique weapon and armor upgrades but the same level requirement rule applies to rare upgrades (both weapons and armors)?

Yes.

Also, could you clarify the meaning of "socket level requirement"?

Suppose you had a Rixot's Keen, upgraded to elite, socketed with a Zod.

The unique has a level requirement of 2. The new base item has a level requirement of 42. The Zod has a level requirement of 69. Because you upgraded it from normal to elite, you add 12 to the level requirement.

That means the final level requirement is max(2, 42, 69) + 12. That is, 81. Without the Zod, it'd require just max(2, 42) + 12 = 54. So, while one might think that adding a 69 level requirement rune in an item would increase the level requirement to 69, this is not the case for upgraded items, since the +5/+7/+12 is added after everything.