According to the Variables index page in the Cross Reference Listing (xref.moodle.org), the variable $SESSION is referenced 717 times, while $session is only referenced 50 times, mostly in the Question module. But try clicking on $SESSION in the Variables list to find ANY of the 717 references. Oh, no you don't! It takes you to the page for $session. The PHP manual plainly states that variable names in PHP are case-sensitive. You would think the Cross Reference Listing would take that into account. It does list the upper- and lower-case names separately, but just try getting to the page for an upper-case name for which there is a variable with the corresponding lower-case name, and you can't get there from here. Too bad. Especially since in general, I would expect the upper-case variables to be much more important. So naturally it's programmed to favor the lower-case names, and cut-off the more important ones. Way to go.