psa_export_key, psa_export_public_key: document the EXPORT flag
diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index 77ade6c..ba2692c 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -733,6 +733,8 @@
* - For public keys (key types for which #PSA_KEY_TYPE_IS_PUBLIC_KEY is
* true), the format is the same as for psa_export_public_key().
*
+ * The policy on the key must have the usage flag #PSA_KEY_USAGE_EXPORT set.
+ *
* \param handle Handle to the key to export.
* \param[out] data Buffer where the key data is to be written.
* \param data_size Size of the \p data buffer in bytes.
@@ -743,6 +745,7 @@
* \retval #PSA_ERROR_INVALID_HANDLE
* \retval #PSA_ERROR_DOES_NOT_EXIST
* \retval #PSA_ERROR_NOT_PERMITTED
+ * The key does not have the #PSA_KEY_USAGE_EXPORT flag.
* \retval #PSA_ERROR_NOT_SUPPORTED
* \retval #PSA_ERROR_BUFFER_TOO_SMALL
* The size of the \p data buffer is too small. You can determine a
@@ -801,6 +804,9 @@
* big-endian byte string. The length of the byte string is the length of the
* base prime `p` in bytes.
*
+ * Exporting a public key object or the public part of a key pair is
+ * always permitted, regardless of the key's usage flags.
+ *
* \param handle Handle to the key to export.
* \param[out] data Buffer where the key data is to be written.
* \param data_size Size of the \p data buffer in bytes.
