Smash

Keep an operand's ink and advance while suppressing its logical height or depth. The baseline stays aligned with the original operand's baseline.

Property	Default	Meaning
children	Empty	Visible operand.
top	true	Suppress height above the baseline.
bottom	true	Suppress depth below the baseline.

top={true} suppresses height above the baseline; bottom={true} suppresses depth below it. Both default to true. Use bottom={false} for \smash[t]{…} and top={false} for \smash[b]{…}. Setting both false keeps the extents.

Smash is an ordinary atom. Its drawing remains in ink/overflow, so a surrounding row does not regain the suppressed line height. Leave room in an explicit SVG viewport for that overhang. Phantom hides ink; Lap removes horizontal advance. See math boxes.