Show notice when using experimental features

examples/edit-geographic.html

@@ -7,6 +7,7 @@ docs: >
   makes it so the map view uses geographic coordinates (even if the view projection is
   not geographic).
 tags: "geographic"
+experimental: true
 ---
 <div id="map" class="map"></div>
 <select id="mode">

examples/templates/example.html

@@ -99,6 +99,12 @@
         This example uses OpenLayers v<span>{{ olVersion }}</span>. The <a id="latest-link" href="#" class="alert-link">latest</a> is v<span id="latest-version"></span>.
       </div>
 
+      <div id="experimental" class="alert alert-warning alert-dismissible" role="alert" style="display:none">
+        <button id="experimental-dismiss" type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">&times;</span></button>
+        This example uses features that are not part of the stable API and subject to change between releases.  Consult the <a href="https://openlayers.org/en/latest/apidoc/">API documentation</a>
+        to see what is supported in the latest release.
+      </div>
+
       <div class="row-fluid">
         <a class="codepen-button pull-right"><i class="fa fa-codepen"></i> Edit</a>
         <div class="span12">
@@ -183,6 +189,15 @@
         document.cookie = cookieText;
       }
     }
+
+    var experimentalNotice = document.getElementById('experimental');
+    if (window.experimental) {
+      experimentalNotice.style.display = 'block';
+      document.getElementById('experimental-dismiss').onclick = function() {
+        experimentalNotice.style.display = 'none';
+      }
+    }
+
   });
   </script>
 </html>

examples/webpack/example-builder.js

@@ -200,6 +200,12 @@ ExampleBuilder.prototype.render = async function(dir, chunk) {
     tag: `<script src="${this.common}.js"></script><script src="${jsName}"></script>`,
     source: jsSource
   };
+
+  if (data.experimental) {
+    const prelude = '<script>window.experimental = true;</script>';
+    data.js.tag = prelude + data.js.tag;
+  }
+
   data.pkgJson = JSON.stringify({
     name: name,
     dependencies: getDependencies(jsSource),