Full database backups represent the database at the time the backup finished
I can't find the same piece of information about the transaction log. From my understanding it would be at the start of it (The log backup would represent the database at the time the log started (using the first LSN)). Every committed transactions will be backup, ongoing transactions would be undo if we were to restore that log backup.
I wish to find if the log backup has the same mechanism as a full backup (data + the transaction log portion while the backup was running) or not.