diff --git a/coap.h b/coap.h
index c67c7ce..58d93b3 100644
--- a/coap.h
+++ b/coap.h
@@ -102,16 +102,40 @@ typedef enum
     COAP_RSPCODE_CHANGED = MAKE_RSPCODE(2, 4)
 } coap_responsecode_t;
 
-//http://tools.ietf.org/html/rfc7252#section-12.3
+// https://www.iana.org/assignments/core-parameters/core-parameters.xhtml#content-formats
+// http://tools.ietf.org/html/rfc7252#section-12.3
 typedef enum
 {
     COAP_CONTENTTYPE_NONE = -1, // bodge to allow us not to send option block
-    COAP_CONTENTTYPE_TEXT_PLAIN = 0,
-    COAP_CONTENTTYPE_APPLICATION_LINKFORMAT = 40,
-    COAP_CONTENTTYPE_APPLICATION_XML = 41,
-    COAP_CONTENTTYPE_APPLICATION_OCTECT_STREAM = 42,
-    COAP_CONTENTTYPE_APPLICATION_EXI = 47,
-    COAP_CONTENTTYPE_APPLICATION_JSON = 50,
+
+    /* 0-255  Expert Review */
+    COAP_CONTENTTYPE_TEXT_PLAIN                   = 0    ,  //  text/plain; charset=utf-8                    /* Ref: [RFC2046][RFC3676][RFC5147] */
+    COAP_CONTENTTYPE_APPLICATION_COSE_ENCRYPT0    = 16   ,  //  application/cose; cose-type="cose-encrypt0"  /* Ref: [RFC8152] */
+    COAP_CONTENTTYPE_APPLICATION_COSE_MAC0        = 17   ,  //  application/cose; cose-type="cose-mac0"      /* Ref: [RFC8152] */
+    COAP_CONTENTTYPE_APPLICATION_COSE_SIGN1       = 18   ,  //  application/cose; cose-type="cose-sign1"     /* Ref: [RFC8152] */
+    COAP_CONTENTTYPE_APPLICATION_LINKFORMAT       = 40   ,  //  application/link-format                      /* Ref: [RFC6690] */
+    COAP_CONTENTTYPE_APPLICATION_XML              = 41   ,  //  application/xml                              /* Ref: [RFC3023] */
+    COAP_CONTENTTYPE_APPLICATION_OCTECT_STREAM    = 42   ,  //  application/octet-stream                     /* Ref: [RFC2045][RFC2046] */
+    COAP_CONTENTTYPE_APPLICATION_EXI              = 47   ,  //  application/exi                              /* Ref: ["Efficient XML Interchange (EXI) Format 1.0 (Second Edition)" ,February 2014] */
+    COAP_CONTENTTYPE_APPLICATION_JSON             = 50   ,  //  application/json                             /* Ref: [RFC4627] */
+    COAP_CONTENTTYPE_APPLICATION_JSON_PATCH_JSON  = 51   ,  //  application/json-patch+json                  /* Ref: [RFC6902] */
+    COAP_CONTENTTYPE_APPLICATION_MERGE_PATCH_JSON = 52   ,  //  application/merge-patch+json                 /* Ref: [RFC7396] */
+    COAP_CONTENTTYPE_APPLICATION_CBOR             = 60   ,  //  application/cbor                             /* Ref: [RFC7049] */
+    COAP_CONTENTTYPE_APPLICATION_CWT              = 61   ,  //  application/cwt                              /* Ref: [RFC8392] */
+    COAP_CONTENTTYPE_APPLICATION_COSE_ENCRYPT     = 96   ,  //  application/cose; cose-type="cose-encrypt"   /* Ref: [RFC8152] */
+    COAP_CONTENTTYPE_APPLICATION_COSE_MAC         = 97   ,  //  application/cose; cose-type="cose-mac"       /* Ref: [RFC8152] */
+    COAP_CONTENTTYPE_APPLICATION_COSE_SIGN        = 98   ,  //  application/cose; cose-type="cose-sign"      /* Ref: [RFC8152] */
+    COAP_CONTENTTYPE_APPLICATION_COSE_KEY         = 101  ,  //  application/cose-key                         /* Ref: [RFC8152] */
+    COAP_CONTENTTYPE_APPLICATION_COSE_KEY_SET     = 102  ,  //  application/cose-key-set                     /* Ref: [RFC8152] */
+    COAP_CONTENTTYPE_APPLICATION_COAP_GROUP_JSON  = 256  ,  //  application/coap-group+json                  /* Ref: [RFC7390] */
+    /* 256-9999  IETF Review or IESG Approval */
+    COAP_CONTENTTYPE_APPLICATION_OMA_TLV_OLD      = 1542 ,  //  Keep old value for backward-compatibility    /* Ref: [OMA-TS-LightweightM2M-V1_0] */
+    COAP_CONTENTTYPE_APPLICATION_OMA_JSON_OLD     = 1543 ,  //  Keep old value for backward-compatibility    /* Ref: [OMA-TS-LightweightM2M-V1_0] */
+    /* 10000-64999  First Come First Served */
+    COAP_CONTENTTYPE_APPLICATION_VND_OCF_CBOR     = 10000,  //  application/vnd.ocf+cbor                     /* Ref: [Michael_Koster] */
+    COAP_CONTENTTYPE_APPLICATION_OMA_TLV          = 11542,  //  application/vnd.oma.lwm2m+tlv                /* Ref: [OMA-TS-LightweightM2M-V1_0] */
+    COAP_CONTENTTYPE_APPLICATION_OMA_JSON         = 11543   //  application/vnd.oma.lwm2m+json               /* Ref: [OMA-TS-LightweightM2M-V1_0] */
+    /* 65000-65535  Experimental use (no operational use) */
 } coap_content_type_t;
 
 ///////////////////////