"may be preferable" instead of "is preferable"

Feedback from PR that this should be more of a suggestion.
We may strengthen later.

Author: handrews

jsonschema-core.xml

@@ -578,7 +578,7 @@
                     <t>
                         Using JSON Pointer fragments requires knowledge of the structure of the schema.
                         When writing schema documents with the intention to provide re-usable
-                        schemas, it is preferable to use a plain name fragment that is not tied to
+                        schemas, it may be preferable to use a plain name fragment that is not tied to
                         any particular structural location.  This allows a subschema to be relocated
                         without requiring JSON Pointer references to be updated.
                     </t>