Comment by scbrg

The page has four sections, divided by <hr> tags;

1) The email message, with a few headers included

2) A thread overview, with all emails in the thread

3) Instructions on how to reply

4) Information about how to access the list archives.

You need only care about (1) and (2). The difference between prev and parent is indicated by the tree view in (2). The previous one is the previous one in the tree, which might not necessarily be the parent if the parent has spawned earlier replies.