Man pages matching name tsmimehdrfieldvaluestringget in section 3ts:

TSMimeHdrFieldValueStringGet.3ts.en	debian 10 / trafficserver-dev
TSMimeHdrFieldValueStringGet.3ts.en	debian 11 / trafficserver-dev
TSMimeHdrFieldValueStringGet.3ts.en	debian 12 / trafficserver-dev