Toggles the editor between standard and source edit mode.
@param {Boolean} [sourceEditMode] True for source edit, false for standard
function(sourceEditMode) {
        var me = this,
            iframe = me.iframeEl,
            textarea = me.textareaEl,
            hiddenCls = Ext.baseCSSPrefix + 'hidden',
            btn = me.getToolbar().getComponent('sourceedit');

        if (!Ext.isBoolean(sourceEditMode)) {
            sourceEditMode = !me.sourceEditMode;
        }
        me.sourceEditMode = sourceEditMode;

        if (btn.pressed !== sourceEditMode) {
            btn.toggle(sourceEditMode);
        }
        if (sourceEditMode) {
            me.disableItems(true);
            me.syncValue();
            iframe.addCls(hiddenCls);
            textarea.removeCls(hiddenCls);
            textarea.dom.removeAttribute('tabIndex');
            textarea.focus();
            me.inputEl = textarea;
        } else {
            if (me.initialized) {
                me.disableItems(me.readOnly);
            }
            me.pushValue();
            iframe.removeCls(hiddenCls);
            textarea.addCls(hiddenCls);
            textarea.dom.setAttribute('tabIndex', -1);
            me.deferFocus();
            me.inputEl = iframe;
        }
        me.fireEvent('editmodechange', me, sourceEditMode);
        me.updateLayout();
    }