We are trying to provide editor to add html data directly into TinyMCE Editor which we use via XHtml String property.
Is there a way to enable HTML directly in the description area for it.
Are you referring to Code button in TinyMCE?
I think Dejan already pointed out that you are most likely looking for the "code" button.
Assuming you are using Episerver TinyMCE version 2.x so here is a link to code how to configure the editor to have the code button.
So in the linked code ".AddPlugin("code")" and the toolbar buttons configuration "code" are the key points how to add the code editing to the editor.