[css-grid] Bug in Example 24, line-based placement

Example 24 says that the placement for:

grid-column-start: 'C'; grid-column-end: 'C';

should be:

/* Line 3 to line 9 */

I believe this is wrong.

grid-column-end: 'C' resolves to the same grid line than
grid-column-start: 'C', which is invalid, so I assume the right thing
to do is fallback to 'auto', and the correct result would be:

/* Line 3 to 4 */

Cheers,

Xan