[css-box][css-shapes][css-masking] half-border-box in Box-Edge Keywords #12965
Description
The Box module specifies several value types of box-edge keyword sets to be used in other specifications:
<visual-box> = content-box | padding-box | border-box<layout-box> = <visual-box> | margin-box<paint-box> = <visual-box> | fill-box | stroke-box<coord-box> = <paint-box> | view-box
Some modules still need to extend these. In particular, css-shapes adds one type that css-masking extends to another one:
<shape-box> = <visual-box> | margin-box | half-border-box<geometry-box> = <shape-box> | fill-box | stroke-box | view-box
However, both of these differ only by the addition of the peculiar half-border-box keyword from one of the predefined subsets of <box>:
<shape-box> = <layout-box> | half-border-box<geometry-box> = <coord-box> | half-border-box
Therefore, I wonder whether that box-edge keyword and the value sets using it should be backported to [css-box] or if those two specialized set definitions should be simplified as shown above in their respective modules.
By the way, <display-box> from css-display is unrelated.