Expected: orange cells span the stated columns; the width of a spanning cell equals the sum of its columns plus the gutters between them. The last row's colspan=9 exceeds the 4-column grid and must not widen the table.
| c1 | c2 | c3 | c4 | |||||
| span 2 | c3 | c4 | ||||||
| c1 | span 3 | |||||||
| span all 4 | ||||||||
| colspan 9 (clamped) | ||||||||