Hey that's really great to hear. (that you're keen to use Kim) WTF-Forms and Marshmallow both solve problems and they do it well but it seems like us you wanted something that offered just a bit more flexibility. That's totally the idea behind pipelines in Kim. They are like tiny little computer programmes and are really capable of anything (providing it's possible in Python of course :D )

It's great you asked this question as we noticed part of the documentation was actually broken. here's a link to a pretty basic example of adding extra validation "pipes" to a pipeline

http://kim.readthedocs.io/en/latest/user/advanced.html#custo...

We'd be more than happy to discuss how to solve more complex requirements if there's something specific you had in mind though.

Thanks for the message!