I'm just saying, as someone who has used subversion quite a lot over the years, the situation he is describing where you have an exclusive lock where they have to check in before you can, does not happen. Exclusive locks are very rarely used in subversion. If you and your coworker are working on a file, and he checks in before you, you will simply have to update and merge. Similar to if you were both working on a local git or mercurial tree.
Oh, and in that situation the 3 way merge is between the version he checked into the repo, your local version you are trying to commit, and your parent revision.
