I want to create a binding with custom functionality. Is this possible to do in Noesis and use it in markup the same way you'd use a regular Binding?

You can add your own markup extensions by extending the MarkupExtension class and overriding the ProvideValue method.

See the official WPF documentation for custom markup extensions: https://learn.microsoft.com/en-us/dotne ... on-classes

If you want to replicate the Binding MarkupExtension's behaviour, or part of it, you'll need to replicate it's functionality in your code. The binding extension itself is not extensible.

If you let me know the functionality you desire I'll give you more information on how it might be achieved.