No joke, if you do a search for "borealis" in windows explorer in "C:\Program Files (x86)\Steam\steamapps\common\SourceFilmmaker\game\hl2", you will get a good amount of stuff. Lots of VTF's.
That whole thing is code I found in a file called "constants.py".
Here's another interesting one I think:
if engine == 'Source':
# Example: C:\Dev\tools\python\generic
pyPath = Path( r'{0}\python\generic'.format( toolsDir, version, arch ) ).unresolved()
else:
#...