I try to limit the input and displayed characters of an AvaloniaUi Textbox to just allow hexadezimal characters. So 0-F. So far I was not able to accomplish by using the various events and handle them in the codebind like TextInput, TextChanged, KeyDown etc. In some cases the eventhandler doesnt even get executet or the e.handle= false/true has no effect and not allowed characters still show up in the textbox. What is the proper and working way to achieve this behaviour?