a small update to the code so that the “more” tag can be inserted when there’s no root block:
c.addCommand("WP_More", function () {
node = c.selection.getNode();
if(node.nodeName != 'BODY') {
p = node;
while(p.parentNode.nodeName != 'BODY')
p = p.parentNode;
var div = c.dom.create('div', {}, f);
c.dom.insertAfter(div.firstChild, p);
}
else {
c.execCommand("mceInsertContent", 0, f);
}
});