demo：

function FCKeditor_OnComplete( editorInstance )
{
editorInstance.EditorDocument.attachEvent("onkeydown", editor_keydown);
editorInstance.EditorDocument.attachEvent("onkeyup", editor_keyup);
}
function editor_keydown()
{
var oEditor = FCKeditorAPI.GetInstance('inputmsg') ;
var keycode = oEditor.EditorWindow.event.keyCode;
if(keycode==13) {

}

}
function clearInput()
{
var oEditor = FCKeditorAPI.GetInstance('inputmsg') ;
oEditor.Commands.GetCommand( "NewPage" ).Execute(); // oEditor.SetHTML("") ;
}

function editor_keyup()
{
var oEditor = FCKeditorAPI.GetInstance('inputmsg') ;
var keycode = oEditor.EditorWindow.event.keyCode;

if(keycode==13) {
clearInput();
}
}