docs: Clarify, not every function that returns int returns -1 for errors.

diff --git a/src/guestfs.pod b/src/guestfs.pod
index da03128..dd06880 100644 (file)
--- a/src/guestfs.pod
+++ b/src/guestfs.pod
@@ -877,8 +877,8 @@ This closes the connection handle and frees up all resources used.
 
 =head1 ERROR HANDLING
 
-The convention in all functions that return C<int> is that they return
-C<-1> to indicate an error.
+API functions can return errors.  For example, almost all functions
+that return C<int> will return C<-1> to indicate an error.
 
 Additional information is available for errors: an error message
 string and optionally an error number (errno) if the thing that failed