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.

addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile