Weak and strong constraints
Constraints can be classified into two categories: Weak and strong. This classification
         determines whether processors enforce strict compatibility during @conref or
         @conkeyref resolution.
      
      - Strong constraints
 - Constraints for which processors enforce strict compatibility during @conref or @conkeyref resolution.
 - Weak constraints
 - Constraints for which a processor does not enforce strict compatibility during @conref or @conkeyref resolution.
 
By default, constraints are weak unless they are explicitly designated as strong.
Any constraint declaration can designate a constraint as strong. A constraint can
            be
            designated as strong by prefixing the letter "s" to the domains attribute contribution,
            for
            example, "s(topic task strictTaskbody-c)". Processors also can be configured
            to treat all constraints as strong.
         
The following behavior is expected of processors:
- Processors MAY perform constraint compatibility checking.
 - If processors perform constraint compatibility checking, they SHOULD enforce strict compatibility for strong constraints.
 - Processors MAY have an option for configuring whether all constraints are treated as strong constraints.