Extensions Warnings should be optimized

[je4]

Initial Extension

As I am using an unregistered initial extension, I feel that spec and validation codes are not entirely clear.

According to https://github.com/OCFL/extensions#optional-initial-extension the initial extension resides in the initial folder in the extensions subdirectory. This causes two problems

1. Warning W013 or W016 is given for registered AND unregistered extensions.
2. If the validator would accept initial as a subdirectory, there would be no warning, even if a Local Extension is used.

Extension directory with registered extension name

If an extension directory is named after a registered extension, but config.json points to a local extension, no warning is given.

Possible solution

Replace

Extension subdirectories SHOULD be named after a registered extension name in the OCFL Extensions repository.

With something like

Extension subdirectories with exception of initial SHOULD use the same name as the extension. Only registered extensions SHOULD be used.

[neilsjefferies]

Editors agree. Spec will be updated.

[neilsjefferies]

Possible, and slightly more elegant, alternative from @awoods would be to simply define an extension with the special name "initial" which explains its function. transferring this ticket to the extensions repository