That site explains the use of negatives well, but I've found a lot of errors in the example sentences. This one has less explanation, but the examples are definitely correct.
Unfortunately I couldn't find a list of the derivatives of sem, but you basically create those words out of interrogative pronouns. The basic formula is se + pronoun. (se + hogy -> sehogy, se + melyik -> semelyik, etc.)
The ones with a little difference:
Mi? -> semmi
Ki? -> senki
Milyen? -> semmilyen
The derivatives of these (semmiért, senkitől, semmilyenre, etc.)
All of the sem-words are used with double negative.
how embarrassing, I am a native speaker and that is what I put. Though it wouldn't be something that would be written in a formal academic composition, it is the kind of thing that is said when frustrated, and sputtering and at your wits end, waiting for a car on the road when you are hitch hiking or broken down.
also, a more rare use of a sentence structure such as "a car doesn't come from anywhere" is when a parent is arguing with their demanding teenager who wants a car as a present. So the parent will say something like, "a car doesn't come from JUST ANYWHERE." Implying, it comes from somewhere, as in it comes from the slaving, hardworking parent's pocketbook, and doesn't come falling from the sky.
It is only "bárhonnan" (or "akárhonnan") in a positive statement. In a negative statement, it is translated as sehonnan. I guess this is due to the fact that English does not like double negatives while Hungarian loves them.
"A car can come from anywhere." - "Bárhonnan jöhet egy autó."
"No car can come from anywhere." - "Sehonnan sem jöhet autó."
I was (apparently mistakenly) thinking "sehonnan" means "nowhere"... So how would you translate "The car came from nowhere" (like in something like "Yes, officer, that damn plane came from nowhere and hit the kindergarten teacher who was peacefully flying around those tall, dark chimneys")?