[css-masking] How does masking apply to table parts?

[dbaron]

The masking spec doesn't say anything about table parts. But in many ways masking is like backgrounds, and then like borders, both of which apply to table parts in very interesting and unusual ways.

Does masking work like backgrounds on, say, table rows? (Is that even well defined?)

If it doesn't, it still needs to define how, say, masking on a row applies to rowspanning cells originating in that row, or rowspanning cells originating in another row that span into that row. It also needs to define what the bounds of the row are for both mask-origin and mask-clip purposes.

etc.

[dirkschulze]

CSS Background and Borders does have specific text on border-image* properties for internal table elements. Specifically to the content model:

Applies to: All elements, except internal table elements when border-collapse is collapse

Furthermore, border-image* has the following additional text:

The border-image properties apply to the border of tables and inline tables that have border-collapse set to collapse. However, this specification does not define how such an image border is rendered. In particular, it does not define how the image border interacts with the borders of cells, rows and row groups at the edges of the table (see border conflict resolution in [CSS2]).

It is expected that a future specification will define the rendering. It is recommended that UAs do not apply border images to tables with collapsed borders until then.

The spec specifically references https://www.w3.org/TR/CSS22/tables.html#propdef-border-collapse

@dbaron I suppose the same restrictions would apply to border-box masks. I could not find additional text or restrictions to backgrounds.