In several images, incuding the most up to date 3.7,
FileDirectory>>openSources:andChanges:forImage:
on the class side (how is that indicate?)
gives this error message

"Squeak cannot locate &fileRef.

Please check that the file is named properly and is in the
same directory as this image.  
Further explanation can found
in the startup window, ''How Squeak Finds Source Code''."

As far as I can tell, there is no such window.  I was looking for one
of the existing titled windows in stock images.

There is a discussion in the the ReadMe.txt window under the subhead
"Sources and Changes" which is relevant.

I have doubts someone approaching squeak for the first time would find
that discussion.  I'm also not sure they would find it useful.

I was actually expecting to see information on how to edit where
squeak things the sources/changes are, but I have a feeling that was
not the intent.