Get parent element from binding behaviour in custom attribute

[jods4]

Issue: it is impossible to get at the parent element from a binding behavior, if the behavior is used inside a custom attribute.

Context: I have built a validation component. It makes use of a binding behavior, which wants to grab the element, in a fashion that is exactly the same as this one from aurelia-validation: https://github.com/aurelia/validation/blob/master/src/validate-binding-behavior.js#L18-L31

The code is slightly complicated, but let's say that's an advanced use. At least it seems possible!

But in practice there are three cases to cover:

• If the behavior is on a regular element/value, e.g. <input value.bind="x & validate"> then binding.target is the input element.
• If the behavior is on a custom element, e.g. <my-input value.bind="x & validate">, then binding.target is the custom element ViewModel. At least, using this we can find out its controller in the enclosing view, which leads us to its element (given it's not @containerless).
• If the behavior is on a custom attribute, e.g. <input my-value.bind="x & validate"> then binding.target is the custom attribute ViewModel. And there we're stuck. We can grab its controller but there is no link to its element.

I have no opinion how this could/should be fixed. Maybe an addition to binding or is that too costly? Otherwise an addition to the attribute controller?

[jdanyow]

https://github.com/aurelia/validatejs/issues/97

[jdanyow]

closing- will be covered in #457