It seems that container is no longer supported as a built-in template:

Template with signature container() not defined container[class := indexprevious {““Previous””}

But then I want to be able to define container as a library template such that it can deal with legacy calls such as the above, i.e. by passing class as an attribute; how do I define such a container template?

Submitted by Eelco Visser on 24 December 2010 at 13:50

built-in.app was old, instance of https://yellowgrass.org/issue/WebDSL/296