I was reading an article today, critical of the Western Rite, in which the author makes the following assertion.
Contrary to the ancient practices of the Church, "Byzantine" clergy visiting "western rite" parishes are not allowed - in current Antiochian practice - to concelebrate (and would hardly know how to, even if permitted). Pan-Orthodox services like the vespers for the Sunday of Orthodoxy are now rendered complex if not downright confusing by the possible presence of "western rite" clergy.
Is this at all true? And, if not, how would concelebration in the author's mooted Pan-Orthodox service work? Assuming that the service was Eastern Rite, would Western Rite clergy be expected to do anything other than just attend? Are there rubrics for this kind of scenario?