introduce a default render implementation on the base widget, which
add_media and then call the newly introduced method
_render(form, field, formrenderer), abstract of the base widget class.
This allow a litle code factorisation and avoid to forget the call to
add_media in subclasses.
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/web usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/share/cubicweb/cubes/shared/data usr/share/cubicweb/cubes/shared
debian/tmp/usr/share/cubicweb/cubes/shared/wdoc usr/share/cubicweb/cubes/shared