How do I add a new session variable?

[carcomp]

I want to know how to add a boolean variable to vbulletin's session. I can't find where they are all declared.

[Dismounted]

<a href="https://vborg.vbsupport.ru/showthread.php?t=152344" target="_blank">[How-To] Extend and use the Session Table Effectively</a>