For ShapeDriven Rebar: returns true, if the Rebar element's external constraints are available for editing using the RebarConstraintsManager class. Examples of where this method would return false are: Rebar in Groups (which do not have constraints), or legacy, sketch-based Rebar elements created before the introduction of RebarShape families in version 2009.

For FreeForm rebar: constraints can be edited if there is a valid external server Guid assigned to that Rebar