Optionalangleinitial rotation in radians; bodies never spin, this is a display offset for sprites
Optionaldensitymass per unit area; 1 when omitted
OptionalfrictionOptionalisan immovable body: ground, anchors
Optionallabela name for collision callbacks and lookups
Optionalrestitution0 to 1, how much of its speed a bounce keeps; 0 when omitted
Per-body material and identity options for
addBox/addCircle.