What is necessary for an attribute to be used in promotions?

For an attribute to be used in promotions, it is essential that it possesses the property of 'Can be used in creating promotions.' This is a specific setting within Magento that enables the attribute to be utilized in the rules and logic of promotional campaigns. Without this property being set, the attribute will not be recognized by the promotion engine, and therefore cannot be leveraged to create targeted promotions, special pricing, or discounts based on that attribute.

Attributes in Magento have various settings that determine how and where they can be used. While visibility on the front end and default values are important for general use, they do not directly relate to the ability of the attribute to contribute to promotional schemes. Similarly, indexing pertains more to performance and data retrieval rather than functional applicability in promotion creation. Hence, setting the property to 'Can be used in creating promotions' is the primary requirement that must be fulfilled for an attribute to assist in promotional efforts.