nsIDOMNSHTMLDocument
); void clear(); boolean execcommand(in domstring commandid, in boolean doshowui, in domstring value); boolean execcommandshowhelp(in domstring commandid); obsolete since gecko 14.0 domstring getselection(); nsidomdocument open(in acstring acontenttype, in boolean areplace); boolean querycommandenabled(in domstring commandid); boolean querycommandindeterm(in domstring commandid); boolean querycommandstate(in domstring commandid); boolean querycommandsupported(in domstring commandid); domstring querycommandtext(in domstring commandid); obsolete since gecko 14.0 domstring querycommandvalue(in domstring commandid); void releaseevents(in long eventflags); void routeevent(in nsidomevent evt); ...
... write to the document will probably throw.
...bably throw.

Midas
section : <html> <head> <title>simple edit box</title> </head> <body> <iframe id="midasform" src="about:blank" onload="this.contentdocument.designmode='on';" ></iframe> </body> </html> methods document.execcommand executes the given command.

Document - Web APIs
cument, executes a formating command.