compilation-finish-function vs compilation-finish-functions

[Drew Adams]

What is the usage difference between `compilation-finish-function' and
`compilation-finish-functions'?

I don't see this explained anywhere. I haven't checked the latest CVS info
files for the Elisp manual, but I have checked the latest compile.el source
code and see no explanation there. Shouldn't the usage be documented
somewhere?

Clearly, a user would generally not use both of these. Is one of them
intended to be deprecated? If not, shouldn't the order of execution (first
`function', then `functions') be advertised?