A WPF Markup Extension for binding to the value of a property on a collection of items - for use in multi-select ListViews.
Okay, this is weird to explain.
Let's say you have a list of items and some editing controls. Instead of selecting one item and changing a value, with this you can select multiple items and change the value of all of them at once. All through the power of binding (and a custom MarkupExtension).
This code is meant as an example, and has not been production tested. Use at your own risk.