Google’s Recommended & Required Properties (Data Attributes)
Although Google utilizes Schema vocabulary, it has also created its own set of recommended and required properties. Each structured data object has a unique set of recommended and required properties, all depending on the type of content and information it is providing.
If an object does not contain all required properties then it will not be eligible for a rich result, in which case Google will alert a Webmaster of this in the GSC Enhancements report.
If an object contains all required properties but is missing some recommended properties then Google will alert a Webmaster of this in the GSC Enhancements report. Important to note that any recommended properties that are not included in the markup will NOT negatively impact the eligibility of the rich result. Regardless, it is still recommended that as many recommended properties be complete as possible to have the greatest effect on the rich result’s performance.