For example, you cannot use the IndexOnly directive with the "prog" document source. This is by design to limit the overhead when using an external program for providing documents to swish; after all, ...

Perl is a messy, maddening programming language, the “duct tape of the internet.” But at least you can tell it was made by humans.

I write Perl programs that use the Windows shell command dir. The dir command is built into cmd.exe and there is no dir.exe in the System folder.