ShapeDriven:

The RebarConstraint should be one of the candidate RebarConstraints returned by getConstraintCandidatesForHandle.

In general, the caller should assume that the 'set' operation can fail, as some of the candidates may be legal targets for the handle, but may cause the rebar to flex into an insoluble shape.

Once a preferred constraint has been successfully assigned to a handle, the user can still drag the handle, and the Rebar can generally be flexed in much the same way as it could before (preferred constraints do not have the same effect as Revit locked dimensions). However, the rebar's behavior will change in subtle ways.

A handle with a FixedDistanceToHostFace preferred constraint will allow the constraint's offset distance to change as the user moves the handle. However, in subsequent model updates, the handle will continue to follow the preferred constraint target, even if other legitimate constraint targets are closer to the handle. One can think of this behavior as equivalent to unlocking a locked dimension, moving one of dimension references, and then re-locking the dimension - all in one step.

When a handle with a ToCover or ToOtherRebar preferred constraint is dragged by the user, it will snap back to its constraint target, unless it is dragged beyond tolerance distance. In that case, it will select a new constraint using default logic, but will continue to treat the "broken" constraint as preferred, and will snap back to the preferred target again, if it is dragged to within tolerance distance.

If, during a model update, the rebar determines that a preferred constraint target no longer exists, or has been modified so that it is no longer a legal candidate for the handle, then the rebar will remove the preferred status of that target and will assign a new constraint to the handle using the default logic.

FreeForm:

Sets the RebarConstraint to be active for the specified RebarConstrainedHandle. The RebarConstrainedHandle needs to be a valid handle for this rebar element.