Allow '{-y}' placeholder

examples/xyz.js

@@ -0,0 +1,40 @@
+goog.require('ol.Attribution');
+goog.require('ol.Map');
+goog.require('ol.View2D');
+goog.require('ol.layer.Tile');
+goog.require('ol.source.OSM');
+goog.require('ol.source.XYZ');
+
+
+var attribution = new ol.Attribution({
+  html: 'Tiles &copy; <a href="http://maps.nls.uk/townplans/glasgow_1.html">' +
+      'National Library of Scotland</a>'
+});
+
+var map = new ol.Map({
+  target: 'map',
+  layers: [
+    new ol.layer.Tile({
+      source: new ol.source.OSM({
+        attributions: [
+          new ol.Attribution({
+            html: 'Tiles &copy; <a href="http://www.opencyclemap.org/">' +
+                'OpenCycleMap</a>'
+          }),
+          ol.source.OSM.DATA_ATTRIBUTION
+        ],
+        url: 'http://{a-c}.tile.opencyclemap.org/cycle/{z}/{x}/{y}.png'
+      })
+    }),
+    new ol.layer.Tile({
+      source: new ol.source.XYZ({
+        attributions: [attribution],
+        url: 'http://geo.nls.uk/maps/towns/glasgow1857/{z}/{x}/{-y}.png'
+      })
+    })
+  ],
+  view: new ol.View2D({
+    center: [-472202, 7530279],
+    zoom: 12
+  })
+});