The Patient Referral Act template contains the following:

participant		0..*	Participant2
@typeCode		1..1	cs	Fixed Value: REFT

The C-CDA R2.1 schematron, interestingly enough, already interprets this in a such-that-it-y sort of way, where you need to have 0 participants OR at least one participant with @typeCode="REFT" (but you can have other participants as long as one of them does):

<sch:assert id="a-1098-32638" test="not(cda:participant) or cda:participant[@typeCode='REFT']">The participant, if present, SHALL contain exactly one [1..1] @typeCode="REFT" Referred to (CodeSystem: HL7ActRelationshipType urn:oid:2.16.840.1.113883.5.1002) (CONF:1098-32638).</sch:assert>

But technically, the way this is written right now implies that no other participant/@typeCodes (like "REFB", for instance, the "referred by" provider) are allowed here, which seems wrong. And we probably ought to clarify the template since the ONC's own validator does, in fact, flag this as an error:

Error - Consol Patient Referral Act MAY contain zero or more [0..*] participant, where its type is Participant (CONF:1098-32635) participant SHALL contain exactly one [1..1] @typeCode="REFT" (CONF:1098-32638)
/ClinicalDocument/component/structuredBody/component[2]/section/entry/act/participant
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