The present mechanism obtains constraints within an interactive environment, associates these constraints with constructs, and then applies these constraints to the constructs when encountering the constructs. The constraints may be saved in metadata associated with the respective construct. The constraints may specify a data type for the construct, a predicate directive, a documentation directive, a parsing directive, a data generation directive, a data validation directive, or an object processing and encoding directive. The constraints are extendable to support other directives. The mechanism allows interactive users to easily specify constraints interactively.