Incomplete interface definitons

[mgedmin]

IControl doesn't define readonly, which looks like part of the API. (Although note that IListControl classes don't have readonly properties.)

IControl.type has a list of values that doesn't mention textarea. I also wonder how it would cope with HTML5 control types such as date etc.

IControl doesn't have id (and the implementation lacks it as well), which is sometimes rather inconvenient.