My mother has decided to make a cake today since my aunt is coming to tea tomorrow.
Source: my English grammar book.
Google gives little results involving the given expression "to come to tea".
Is it some kind of an idiom (I understand the meaning, so don't explain it)?
Or is it just something that follows a particular grammar rule?
It really does look unusual when it is looked at from the grammar point of view (no one just "goes directly to tea"; they "go somewhere for tea" instead, i.e. they "go somewhere to get some tea").
So how could you explain the grammar of this? As I said in my last paragraph, the grammar looks unusual, and I want to understand the grammar aspects of this.
I've posted the question “My aunt is coming to dinner tomorrow” (grammar of 'to dinner') on EL&U because I would like to have an answer that show some sources that explain the grammar of this sort of phrase.