ISSUE-227: Added warning on the state of EXISTS

shacl/index.html

@@ -740,6 +740,11 @@ <h3>Relationship between SHACL and SPARQL</h3>
 					The variable <code>shapesGraph</code> can also be used in <a href="#sparql-constraints">SPARQL-based constraints</a> and <a href="#sparql-constraint-components">SPARQL-based constraint components</a>.
 					However, such <a>constraints</a> may not be interoperable across different SHACL-SPARQL processors or not applicable to remote RDF datasets.
 				</p>
+				<p>
+					Note that at the time of writing, SPARQL EXISTS has been imperfectly defined and implementations vary.
+					While a <a href="https://www.w3.org/community/sparql-exists/">W3C Community Group</a> is working on improving this situation,
+					users of SPARQL are advised that the use of EXISTS may have inconsistent results and should be approached with care.
+				</p>
 				<div class="syntaxmenu">
 					<p>The button below can be used to show or hide the SPARQL definitions.</p>
 					<form>