Chrome execCommand returns error

How do I use the execCommand() in Chrome? Here is the code I have right now It is being used to insert a special character when hitting the tab button

function editAble(supr){
    document.getElementById('codeline').contentEditable='true';
    document.getElementById('codeline').onkey开发者_StackOverflow中文版down=function(e)
        {

        if(e.keyCode==9){
            e.preventDefault();
            range1 = document.getElementById('codeline');
            range1.execCommand("InsertHtml",false,"p");

        }
    }
}

The execCommand() method is a method of Document objects, not elements. IE also provides execCommand() as a method of its TextRange and ControlRange objects, but these are not present in other browsers.

document.execCommand("InsertHtml", false, "p");

You may want to consider what happens if the user presses the Tab key when the user has previously selected some text: in that case you'd probably want to delete the contents of the selection before inserting your tab character.