Negative values and keywords for rowspan and colspan #13162

What is the issue with the HTML Standard?

Attributes common to td and th elements specifies colspan and rowspan values as integers with specific limits:

• colspan: (0, 1000]
• rowspan: [0, 65534]

  the value zero means that the cell is to span all the remaining rows in the row group.

While the quoted behavior is useful to have (though little known), accessing it by specifying 0 is as surprising as not having it for columns. A keyword would be better.
Also, there are cases where authors don’t want a cell to span the rest of the group but the whole table dimension – this violates the technical principle that spanned slots must be within the same row group (but may be in a different column group), though.

Proposal

• Add the zero behavior to colspan as well.
• Add the absolute keyword group (or separate rowgroup and colgroup) as an alias of 0.
• Add the absolute keyword table, rest, all or * (at least to colspan), which makes the cell span all remaining slots within the row or column.
• Add behavior for negative integers: the cell is spanned until the nth-last column or row of the table (or group?) unless the starting slot index is already this number or beyond.
  • As a corollary, the keyword from the previous bullet point becomes an alias of -1.
• Add the absolute keyword cell (or separate row and col) as an alias of 1.
• Add the relative keyword scope or auto which computes a value based on the value of the scope attribute:

  • scope	rowspan	colspan
    row ⇒	1 or cell	0 or group
    col ⇒	0 or group	1 or cell
    rowgroup ⇒	0 or group	-1 or all
    colgroup ⇒	-1 or all	0 or group