How can I see the code of a built-in function? I'd like to look at the code of functions such as upcase-region. I looked at the completion list that I pulled up by "find-library TAB", but the list is huge and couldn't figure out if what I'm looking for is included in it or not.
I also looked at the help of upcase-region, and it says
upcase-region is an interactive built-in function in `C source code'.
But when I click the link `C source code', it just brings up a file selecting window with the .emacs.d folder opened, but there doesn't seem to be any file with the .c extension?