$re = '/<PurposeOfUse csd-code=\"(?<ATNAPurposeOfUse>.+?)\"/m';
$str = '2677 <85>1 2021-01-20T11:59:04+00:00 localhost icw-chr 1436 IHE+RFC-3881 - <?xml version="1.0" encoding="UTF-8"?><AuditMessage><EventIdentification EventActionCode="R" EventDateTime="2021-01-20T11:59:04.678Z" EventOutcomeIndicator="8"><EventID csd-code="110106" codeSystemName="DCM" originalText="Export" /><EventTypeCode csd-code="ITI-43" codeSystemName="IHE Transactions" originalText="Retrieve Document Set" /><PurposeOfUse csd-code="NORM" codeSystemName="2.16.756.5.30.1.127.3.10.5" originalText="Normal Access" /></EventIdentification><ActiveParticipant UserID="https://api.test.xad.ch/pxs/webservices/xca/initiatingGateway/iti43RetrieveDocuments" UserName="svrz1975.spital.so.ch" UserIsRequestor="false" NetworkAccessPointID="10.250.76.81" NetworkAccessPointTypeCode="2"><RoleIDCode csd-code="110153" codeSystemName="DCM" originalText="Source Role ID" /></ActiveParticipant><ActiveParticipant UserID="<7601003961638@xua.hin.ch>" UserName="<7601003961638@xua.hin.ch>" UserIsRequestor="true"><RoleIDCode csd-code="HCP" codeSystemName="2.16.756.5.30.1.127.3.10.6" originalText="Behandelnde(r)" /></ActiveParticipant><ActiveParticipant UserID="7601003961638" UserName="Marco Studer" UserIsRequestor="true"><RoleIDCode csd-code="HCP" codeSystemName="2.16.756.5.30.1.127.3.10.6" originalText="Behandelnde(r)" /></ActiveParticipant><ActiveParticipant UserID="http://www.w3.org/2005/08/addressing/anonymous" AlternativeUserID="1436" UserIsRequestor="false" NetworkAccessPointID="api.test.xad.ch" NetworkAccessPointTypeCode="1"><RoleIDCode csd-code="110152" codeSystemName="DCM" originalText="Destination Role ID" /></ActiveParticipant><AuditSourceIdentification AuditEnterpriseSiteID="2.16.756.5.30.1.194" AuditSourceID="t01-x-chrapp-1"><AuditSourceTypeCode csd-code="9" codeSystemName="DCM" originalText="Other" /></AuditSourceIdentification><ParticipantObjectIdentification ParticipantObjectID="761337610339478800^^^&2.16.756.5.30.1.127.3.10.3&ISO" ParticipantObjectTypeCode="1" ParticipantObjectTypeCodeRole="1"><ParticipantObjectIDTypeCode csd-code="2" codeSystemName="RFC-3881" originalText="Patient Number" /></ParticipantObjectIdentification><ParticipantObjectIdentification ParticipantObjectID="2.25.319915379891245844588550626280213087638" ParticipantObjectTypeCode="2" ParticipantObjectTypeCodeRole="3"><ParticipantObjectIDTypeCode csd-code="9" codeSystemName="RFC-3881" originalText="Report Number" /><ParticipantObjectDetail type="Repository Unique Id" value="Mi4xNi43NTYuNS4zMC4xLjE5NC4zLjMuMg==" /><ParticipantObjectDetail type="ihe:homeCommunityID" value="dXJuOm9pZDoyLjE2Ljc1Ni41LjMwLjEuMTk0" /></ParticipantObjectIdentification></AuditMessage>
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php