Improve wording of Svpbmt clarification

src/supervisor.adoc

@@ -1855,10 +1855,12 @@ Non-cacheable, non-idempotent, strongly-ordered (I/O ordering), I/O +
 _Reserved for future standard use_
 |===
 
-Implementations might override additional PMAs not explicitly listed in
+Implementations may override additional PMAs not explicitly listed in
 <<pbmt>>.
-For example, a misaligned memory access to a page with PBMT=IO might raise an
-exception, even if the same access would have succeeded for PBMT=PMA.
+For example, to be consistent with the characteristics of a typical I/O region,
+a misaligned memory access to a page with PBMT=IO might raise an exception,
+even if the underlying region were main memory and the same access would have
+succeeded for PBMT=PMA.
 
 [NOTE]
 ====