In the latest version, you say: “Performer google event header is added if a custom field with name “performer” and purpose “event” exists and has a non-empty value for the event”,
I understand the “performer” part of the comment.
I do not understand what you mean by:
a) purpose “event” exists; and
b) has a non-empty value for the event
Many thanks for explaining, perhaps with an example, what you mean by the latter two clauses.