Update jsonschema-core.md

Author: gregsdennis

jsonschema-core.md

@@ -2246,7 +2246,7 @@ determines the canonical nature of the resulting full IRI.[^18]
 and direct you to read the CREF located in {{#embedded}} for further comments.
 
 While the following IRIs do correctly indicate specific schemas, per the reasons
-outlined in {{embedded}}, they are to be avoided:
+outlined in {{embedded}}, they are to be avoided as they may not work in all implementations:
 
 Document location `/$defs/B`:
 - canonical (and base) `IRI: https://example.com/other.json`