This new warning will only be seen if the document remains in HTML5 mode,
where the summary attribute is obsolete. The W3C validator flags this as
an error, and suggests 'Consider describing the structure of the table in
a caption element or in a figure element containing the table; or simplify
the structure of the table so that no description is needed'.
At the same time this patch also restored the old warning if the document
is HTML4--, if the table element lacks a summary attribute. This has been
a tidy warning since the beginning of time, although the W3C validator
does not presently flag this.
