This video explains how you can write a SharpDevelop addin that provides a tab page "Preview" that displays .html files.

Tutorial2.wmv (3.25 MB, 07:25 m)

The video starts with opening the AddIn created in tutorial 1, so make sure you watch that first.

I hope these tutorials will help some developers getting started with AddIn development so SharpDevelop 2 will have a number of AddIns available.