README.md in sparql-3.2.0 vs README.md in sparql-3.2.1

@@ -279,9 +279,11 @@
     query = SPARQL.parse("SELECT * WHERE { ?s ?p ?o }")
     query.to_sxp #=> (bgp (triple ?s ?p ?o))
 
 ### Parsing a SSE to SPARQL query or update string to SPARQL
 
+    # Note: if the SSE uses extension functions, they either must be XSD casting functions, or custom functions which are registered extensions. (See [SPARQL Extension Functions](#sparql-extension-functions))
+
     query = SPARQL::Algebra.parse(%{(bgp (triple ?s ?p ?o))})
     sparql = query.to_sparql #=> "SELECT * WHERE { ?s ?p ?o }"
 
 ### Command line processing