Example for supporting zope.interface Interface-based dispatch

[moshez]

I have an example for interfacing reg with zope.interface https://gist.github.com/moshez/cb020469eb3bf7c43240b17f8cf87a62
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It would be really useful if it was easier to make custom matchers...for example, if index was an optional argument to match_instance so that I could override it without playing these games.