diff --git a/library/pk_internal.h b/library/pk_internal.h
index a1a34ad..e86a3a0 100644
--- a/library/pk_internal.h
+++ b/library/pk_internal.h
@@ -128,9 +128,58 @@
     return MBEDTLS_PK_IS_RFC8410_GROUP_ID(id);
 }
 
+/*
+ * Set the group used by this key.
+ *
+ * [in/out] pk: in: must have been pk_setup() to an ECC type
+ *              out: will have group (curve) information set
+ * [in] grp_in: a supported group ID (not NONE)
+ */
 int mbedtls_pk_ecc_set_group(mbedtls_pk_context *pk, mbedtls_ecp_group_id grp_id);
+
+/*
+ * Set the private key material
+ *
+ * [in/out] pk: in: must have the group set already, see mbedtls_pk_ecc_set_group().
+ *              out: will have the private key set.
+ * [in] key, key_len: the raw private key (no ASN.1 wrapping).
+ */
 int mbedtls_pk_ecc_set_key(mbedtls_pk_context *pk, unsigned char *key, size_t key_len);
+
+/*
+ * Set the public key.
+ *
+ * [in/out] pk: in: must have its group set, see mbedtls_pk_ecc_set_group().
+ *              out: will have the public key set.
+ * [in] pub, pub_len: the raw public key (an ECPoint).
+ *
+ * Return:
+ * - 0 on success;
+ * - MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the format is potentially valid
+ *   but not supported;
+ * - another error code otherwise.
+ */
 int mbedtls_pk_ecc_set_pubkey(mbedtls_pk_context *pk, const unsigned char *pub, size_t pub_len);
+
+/*
+ * Derive a public key from its private counterpart.
+ * Computationally intensive, only use when public key is not available.
+ *
+ * [in/out] pk: in: must have the private key set, see mbedtls_pk_ecc_set_key().
+ *              out: will have the public key set.
+ * [in] prv, prv_len: the raw private key (see note below).
+ * [in] f_rng, p_rng: RNG function and context.
+ *
+ * Note: the private key information is always available from pk,
+ * however for convenience the serialized version is also passed,
+ * as it's available at each calling site, and useful in some configs
+ * (as otherwise we would have to re-serialize it from the pk context).
+ *
+ * There are three implementations of this function:
+ * 1. MBEDTLS_PK_USE_PSA_EC_DATA,
+ * 2. MBEDTLS_USE_PSA_CRYPTO but not MBEDTLS_PK_USE_PSA_EC_DATA,
+ * 3. not MBEDTLS_USE_PSA_CRYPTO.
+ */
 int mbedtls_pk_ecc_set_pubkey_from_prv(mbedtls_pk_context *pk,
                                        const unsigned char *prv, size_t prv_len,
                                        int (*f_rng)(void *, unsigned char *, size_t), void *p_rng);