[plt-scheme] MrEd: looking for a "flow" layout panel

Has anyone implemented a panel (or other container widget) that lays
out its children in a "flow" manner, i.e. horizontally left to right
to the edge of the widget, then spilling out into the next row(s), and
re-wrapping when the widget is resized?  I didn't see anything on the
Add-Ons page (http://www.cs.utah.edu/plt/develop/).

I imagine the editor widgets do something like this, but probably only
for text?  I haven't delved too deeply into that portion of the
manual.  Anyway, I don't need all the other editor functionality so
that would probably be overkill.

While I'm asking, does anyone have any other handy container/layout
widgets?  Like grid or grid-bag?

--dougo at ccs.neu.edu