nsIDOMNSHTMLDocument
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); void write(); obsolete since gecko 2.0 void writeln(); obsolete since gecko 2.0 attributes attribute type description alinkcolor domstring same as body.alink bgcolor domstring same as body.bgcolor comp...
...querycommandvalue() domstring querycommandvalue( in domstring commandid ); parameters commandid the name of the command to query.

TextRange - Web APIs
textrange.querycommandvalue() returns the domstring indicating the current value of the specified command.
... you can also see document.querycommandvalue().

Midas
document.querycommandvalue determines the current value of the document, range, or current selection for the given command.

Document - Web APIs
document.querycommandvalue() returns the current value of the current range for a formating command.