@displayName shall be "all children of "Specimen (specimen)""
or
The value of @code shall be drawn from value set 2.16.840.1.113883.1.11.16040 EntityCode (2014‑03‑26)
or
The value of @code shall be drawn from value set 2.16.840.1.113883.1.11.16041 MaterialEntityClassType (2014‑03‑26)
Example
example for specimen, coded by SCT
<playingEntity> <codecode="373102004"codeSystem="2.16.840.1.113883.6.96"displayName="Specimen from breast obtained by image guided core biopsy (specimen)"codeSystemName="SNOMED CT"/></playingEntity>