This hook is called when creating a summary mode buffer.

This is called as the last thing before doing the threading and the generation of the summary buffer. It's quite convenient for customizing the threading variables based on what data the newsgroup has. This hook is called from the summary buffer after most summary buffer variables have been set.

It is called after the summary buffer has been generated. You might use it to, for instance, highlight lines or modify the look of the buffer in some other ungodly manner. I don't care.

When Gnus discovers two articles that have the same Message-ID, it has to do something drastic. No articles are allowed to have the same Message-ID, but this may happen when reading mail from some sources. Gnus allows you to customize what happens with this variable. If it is nil (which is the default), Gnus will rename the Message-ID (for display purposes only) and display the article as any other article. If this variable is t, it won't display the article---it'll be as if it never existed.