What is efocus.clw and why do I get a compile error on it?

what is efocus.clw and why do I get a compile error on it?
I have done a search of my computer and do not find this file and yet all my apps have it in the solution list.
I did not put it there but apparantly it is needed because it comes back in the list when I delete it. But with a compile error as the file does not exist.
How do I get it back?

efocus.inc and clw (in libsrc\win folder) implement “Enhanced Focus” and “Enter By Tab” features (Global Properties-App Settings).

It would appear that my efocus.clw has gone missing. I did find one in a backup folder that I copied and all appears to be working.
Thanks for your help.