DOC: Extend the description of EVP_PKEY_CTX_new_from_name()
This adds text the should lead the user to documentation on different
KEYMGMT implementations.
@@ -32,7 +32,8 @@ The EVP_PKEY_CTX_new_from_name() function allocates a public key algorithm
context using the library context I<libctx> (see L<OPENSSL_CTX(3)>), the
key type specified by I<name> and the property query I<propquery>. None
of the arguments are duplicated, so they must remain unchanged for the
-lifetime of the returned B<EVP_PKEY_CTX> or of any of its duplicates.
+lifetime of the returned B<EVP_PKEY_CTX> or of any of its duplicates. Read
+further about the possible names in L</NOTES> below.
The EVP_PKEY_CTX_new_from_pkey() function allocates a public key algorithm
context using the library context I<libctx> (see L<OPENSSL_CTX(3)>) and the
@@ -52,16 +53,14 @@ If I<ctx> is NULL, nothing is done.
=head1 NOTES
-=over 4
-
-=item 1.
+=head2 On B<EVP_PKEY_CTX>
The B<EVP_PKEY_CTX> structure is an opaque public key algorithm context used
by the OpenSSL high level public key API. Contexts B<MUST NOT> be shared between
threads: that is it is not permissible to use the same context simultaneously
in two threads.
-=item 2.
+=head2 On Key Types
We mention "key type" in this manual, which is the same
as "algorithm" in most cases, allowing either term to be used
@@ -69,6 +68,29 @@ interchangeably. There are algorithms where the I<key type> and the
I<algorithm> of the operations that use the keys are not the same,
such as EC keys being used for ECDSA and ECDH operations.
+Key types are given in two different manners:
+
+=over 4
+
+=item Legacy NID or EVP_PKEY type
+
+This is the I<id> used with EVP_PKEY_CTX_new_id().
+
+These are B<EVP_PKEY_RSA>, B<EVP_PKEY_RSA_PSS>, B<EVP_PKEY_DSA>,
+B<EVP_PKEY_DH>, B<EVP_PKEY_EC>, B<EVP_PKEY_SM2>, B<EVP_PKEY_X25519>,
+B<EVP_PKEY_X448>, and are used by legacy methods.
+
+=item Name strings
+
+This is the I<name> used with EVP_PKEY_CTX_new_from_name().
+
+These are names like "RSA", "DSA", and what's available depends on what
+providers are currently accessible.
+
+The OpenSSL providers offer a set of key types available this way, please
+see L<OSSL_PROVIDER-FIPS(7)> and L<OSSL_PROVIDER-default(7)> and related
+documentation for more information.
+
=back
=head1 RETURN VALUES
