I think this is the big thing the previous poster is missing. The technical writer isn't going to go out in the wilderness with a copy of the source, assume the

I think this is the big thing the previous poster is missing. The technical writer isn't going to go out in the wilderness with a copy of the source, assume they understand it after reading it once, write the documentation, and hit publish. Broadly, good writing (even poetry, fiction, and creative non-fiction) has a deceptive amount of research involved. One of the subtle skills of a good writer is knowing what they don't know, and knowing how to fill the gap. Whether they're flagging things they don't understand as they go and resolving them in bulk, or regularly checking their understanding with maintainers as they encounter problems, a good technical writer isn't going to just pretend they understand.