The oneOf constraint on a property means that its value is restricted to matching exactly one of the subschemas.

This should probably follow the same pattern as the existing enum property validation where:

• Adding a new schema to oneOf to an existing oneOf constraint is only OK if it does not result in existing valid values match an existing subschema and the new schema. Default to breaking.
• Adding a net-new oneOf constraint is breaking
• Removing a oneOf schema is breaking