It's working fine now.
My mistake was that somewhere on the page I was doing this action:
RootPanel root = RootPanel.get("content");
so instead of doing this, I did:
And now I am able to write
HTML myHtml = HTML.wrap(element); // element retrieved by GQuery.
So my problem is solved.
However, I cannot now add widgets to the element : <div id="content"></
using root.add(new HTML());
Why is that? any workarounds ?