How to get HTML tags to appear as HTML and not as plain text in a Rich Text Box

Following the code:-


MainDataSource.CreateNavigator().SelectSingleNode("//my:rtfField", NamespaceManager).AppendChild("<h2 xmlns=\"http://www.w3.org/1999/xhtml\">Header Text</h2><p xmlns=\"http://www.w3.org/1999/xhtml\">This is some paragraph text.</p>");