为属性指定取值范围。
@Range(min, max)
@Range min, max
@Range(1, 20)
attr floors = 5
@StartRule
Lot --> primitiveCube(6, 0.2, 6)
extrude(floors * 3)
comp(f) { top: Roof | side: Wall }
Roof --> color(0.5, 0.25, 0.15)
Wall --> color(0.75, 0.72, 0.68)