The specification currently defines transformable HTML elements to be only block-level and atomic inline-level elements.  This excludes all table-related display types except table and inline-table: table-*-group, table-row, table-caption, and table-cell, as well as table-column and table-column-group.  Testing in browsers (IE10 Developer Preview, Firefox 13.0a1, Chrome 19 dev, Opera Next 12.00 alpha) shows the following support:

table-caption: supported by all
table-cell: supported by IE, Firefox, Chrome but not Opera
table-*-group, table-row: supported by Firefox and Chrome, but not IE or Opera

Firefox/Chrome make the most sense to me.  I suggest we change

"""
A transformable element in the HTML namespace which is either a block-level or atomic inline-level element;
"""

to

""
A transformable element is an element in the HTML namespace which is either a block-level or atomic inline-level element, or an element whose 'display' property computes to 'table-row', 'table-row-group', 'table-header-group', 'table-footer-group', 'table-cell', or 'table-caption';
"""

(I didn't see a nicer way to define this in CSS 2.1.)

Any objections?