Rename the AllergyIntolerance 'substance' element to 'code'. Rename the allergyintolerance-substance-code value set to allergyintolerance-code and update the definition to add SNOMED CT allergy and intolerance disorder (condition) codes and the complete "No known allergy" hierarchy. Add a 'substanceExposureRisk' complex extension as a more structured and flexible alternative to 'code'. Update the documentation to reflect these changes.

These changes are consistent with multiple recent discussions and votes in the Patient Care WG, and input from the Patient Care Negation Requirements and TermInfo project discussions.