For example in this sentence:
Brett reads a massive textbook, scribbling notes at his desk.
The second park,
scribbling notes at his desk, has to be some sort of dependent clause because it can't stand on it's own. But is it valid or do you need some sort of conjunction, like replacing the comma with "while" or something similar?
Someone said a phrase like this might be considered an adverbial clause or something similar but I'm not familiar with them. I feel like the sentence format is common, but is it correct? Thanks!