FileExtension & DirectoryIndex can be confusing

[wjdp]

The FileExtension option is used to set which files are picked up by the document store (i.e. which files will be treated as HTML documents and tested). The DirectoryIndex option sets the name of the document which is the root of a directory (i.e. index.html).

Issue is to use another extension you need to set both:

FileExtension: .htm
DirectoryIndex: index.htm

If you don't set DirectoryIndex you get confusing errors like: target is a directory, no index --- index.htm --> subfolder/

I can think of three options to fix this, we can implement one or more as a combination.

1. Remove the extension from DirectoryIndex (i.e. index) and do DirectoryIndex + FileExtension to get the index document. This is the cleanest but I think makes DirectoryIndex harder to understand.
2. Warn / throw an error if the extension of FileExtension and DirectoryIndex do not match.
3. Automatically adjust the extension of DirectoryIndex from FileExtension if the former is not explicitly set.

At the moment I'd go for a combo of 2 & 3.