bytecomp-version-regexp is a variable defined in `C source code'.
Its value is
"^;;;.\\(in Emacs version\\|bytecomp version FSF\\)"

Regular expression matching safe to load compiled Lisp files.
When Emacs loads a compiled Lisp file, it reads the first 512 bytes
from the file, and matches them against this regular expression.
When the regular expression matches, the file is considered to be safe
to load. See also `load-dangerous-libraries'.