Finding details of the NSError webkit domain

I am unable to find the details of the NSError webkit domain, including the definition of 开发者_如何转开发the error codes in this domain. A search in the iOS docs yields nothing, nor a search here on SO, or in the iOS forums. I think this ought to be in a header file, but I'm unsure how to find it. Where can I find this info?

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How about the WebKit Constants Reference

The header file you are looking for is the cunningly named WebKitErrors.h