This is an extension that adds filters at the bottom of XAML intellisense popup - to make it similar to the C# intellisense popup
The code for this extension can be found at https://github.com/npolyak/VSIXRoslynTESTS/tree/master/NP.XAMLIntellisenseExtensionForVS2017.
Here is the link to the article describing how to build such extension: https://www.codeproject.com/Articles/1216579/Implementing-Custom-XAML-Intellisense-VS-Extension
I missed the filters from Karl Shifflett's intellisense extension for VS 2015 and built my own XAML extension for VS2017. Great thanks to Karl - I learned how to build such extensions by looking at his code at https://github.com/Oceanware/XAMLIntelliSensePresenter2015.