[samarudge]

I guess it depends on one's perspective. You are probably right that someone will send a pull request to add it if it's not there, but I think authors of tools should always do their best to encourage users to do things correctly, especially issues like this which can easily be found without even knowing it's an issue (Google-ing "Email Regular Expression" brings up results for me on the first page recommending it's not a good idea)

Certainly when it comes to security, authors should do their best to ensure users of the tool are educated, when there's a security issue with any large software product, particularly open source, that's mostly down to poor configuration or ill-informed users, the authors are instantly criticized, but I think it should be the same for any general features in a tool that targets a specific functionality. This particular "best practice" is quite easy to find, and the tool is very specifically targeted towards validation, yet has something that's against best practice and could potentially cause frustration for people who use this tool, and people who use the stuff created using this tool.