adapts the doc about possible queries to cover the fix for #376

docs/doc/queries.html

@@ -81,7 +81,7 @@ <h2>Source Assignments</h2>
                 <li>The <code>WHERE</code> clause of the query must not contain any other <code>VALUES</code> clause.</li>
             </ul>
             <p>
-                Given such a query, HeFQUIN rewrites the query pattern of the query by applying the solution mappings of the <code>VALUES</code> clause to the <code>SERVICE</code> clauses and, then, removing the <code>VALUES</code> clause. If the <code>VALUES</code> clause contains multiple solution mappings, then the group of <code>SERVICE</code> clauses is copied for each of these solution mappings, and the resulting groups are combined via <code>UNION</code>.
+                Given such a query, HeFQUIN rewrites the query pattern of the query by applying the solution mappings of the <code>VALUES</code> clause to the <code>SERVICE</code> clauses and, then, removing the <code>VALUES</code> clause. If the <code>VALUES</code> clause contains multiple solution mappings, then the group of <code>SERVICE</code> clauses is copied for each of these solution mappings, and the resulting groups are combined via <code>UNION</code>. Additionally, in any of the two cases (just one solution mapping in the <code>VALUES</code> clause or multiple), <code>BIND</code> clauses are added to still capture the bindings for the variables of the <code>VALUES</code> clause.
             </p>
             <p>
                 As an example, consider the following query.
@@ -105,11 +105,15 @@ <h2>Source Assignments</h2>
   {
     SERVICE ex:endpoint1 { .. some pattern (that neither mentions ?s1 nor ?s2) .. }
     SERVICE ex:endpoint2 { .. also some pattern (that also doesn't mention ?s1 or ?s2) .. }
+    BIND (?s1 AS ex:endpoint1)
+    BIND (?s2 AS ex:endpoint2)
   }
   UNION
   {
     SERVICE ex:endpoint1 { .. some pattern (that neither mentions ?s1 nor ?s2) .. }
     SERVICE ex:endpoint3 { .. also some pattern (that also doesn't mention ?s1 or ?s2) .. }
+    BIND (?s1 AS ex:endpoint1)
+    BIND (?s2 AS ex:endpoint3)
   }
 }</code></pre>