Allow adding custom MarkupExtensions for cleaner code.
"This idea is planned, updated over 1 years ago" !! Come on ...
What about the progress?
I downloaded the Beta and It's there!!!
Plus it's an interface, not a class!! now can be combined with DependecyObject!!!
One thing is missing tho, the ConstructorArgumentAttribute.
1) Very important
2) MarkupExtension should be an interface IMarkupExtension so it can be combined with other base classes as DependencyObject etc, I see no point of having MarkupExtension as a class. See http://dotnet.uservoice.com/forums/40583-wpf-feature-suggestions/suggestions/478820 as well
Indeed a very important feature.