SOFTIMAGE|3D expressions and constraints import into XSI, but the order in which they are evaluated is different. For example, in SOFTIMAGE|3D you can apply a direction constraint to an object and also assign an expression to the object that controls its Y rotation. In XSI, you can do this as well, but only the constraint will work.
When you import an object into XSI that uses both a constraint and an expression, messages appear in the command log suggesting how you can replace the constraints with expressions so that the object will behave as it did in SOFTIMAGE|3D. For example:
WARNING : "3093 - The following expression(s) could be created to compensate for a constraint: WARNING : "3055 - PosConst_ExpY_1-0.cube1.kine.global.posx = PosConst_ExpY_1-0.cone1.kine.global.posx WARNING : "3055 - PosConst_ExpY_1-0.cube1.kine.global.posz = PosConst_ExpY_1-0.cone1.kine.global.posz WARNING : "3094 - CnsPos on cube1 could be replaced with the previous expression(s)
SOFTIMAGE|XSI v.6.01