pem_password_cb: Clarify the documentation on passphrases
@@ -335,7 +335,7 @@ I<klen> bytes at I<kstr> are used as the passphrase and I<cb> is
ignored.
If the I<cb> parameters is set to NULL and the I<u> parameter is not
-NULL then the I<u> parameter is interpreted as a null terminated string
+NULL then the I<u> parameter is interpreted as a NUL terminated string
to use as the passphrase. If both I<cb> and I<u> are NULL then the
default callback routine is used which will typically prompt for the
passphrase on the current terminal with echoing turned off.
@@ -355,7 +355,8 @@ value as the I<u> parameter passed to the PEM routine. It allows
arbitrary data to be passed to the callback by the application
(for example a window handle in a GUI application). The callback
I<must> return the number of characters in the passphrase or -1 if
-an error occurred.
+an error occurred. The passphrase can be arbitrary data; in the case where it
+is a string, it is not NUL terminated. See the L</EXAMPLES> section below.
Some implementations may need to use cryptographic algorithms during their
operation. If this is the case and I<libctx> and I<propq> parameters have been
