Re. Control vs Panel, I don't think it would make a lot of difference. Panel inherits from Control. The Panel class adds some handy properties such as a BorderStyle, and it also inherits from ScrollableControl which could be useful.
Just my take on why you should use Control as the base class...
* As I see it the panel control is used to store multiple controls under one grouping not just one. Although I can see in some cases you may want to do this.
* The HTMLDocument class already supports scrollbars.
* It would make the control more flexible. If I want to place the control in a panel to get a BorderStyle then I can do that from the designer or in code. Gives the developer more options.
* In my own code I have had problems placing the HTMLEditor control within a panel with other controls. I could'nt get it to display, I had to recompile with the base class set to Control.
I don't think there are any drawbacks, that I can see, only advantages; it seems a better choice.
Lutz Roeder's original demo of MSHTML hosting used Panel. I did at one time change it to Control, but for a reason I cannot recall, I changed it back. If it was just BorderStyle, then I take your point, and it ought to revert to Control.
Unless you or I find some snags, I'll go to Control in the next update.