I tried dominique calcinelli's suggestion but could not figure out how to get around this error:
Node cannot be inserted at the specified point in the hierarchy
So I eneded up just making an <hr/> with HTML Widget instead, per this other related discussion:
https://groups.google.com/forum/#!topic/Google-Web-Toolkit/NMjozOU4UXkOn Friday, February 22, 2013 11:46:26 AM UTC-5, dominique calcinelli wrote:
First create the HTML <hr/> tag :
InlineHTML hrTag = new InlineHTML().wrap(Document.get().createHRElement());
Then use it as follows :
myPanel.add(hrTag);