Improve docs for projection

examples/wms-image-custom-proj.js

@@ -12,6 +12,10 @@ goog.require('ol.source.ImageWMS');
 // known to Proj4js if it is unknown to OpenLayers, and registers functions to
 // transform between all registered projections.
 // EPSG:21781 is known to Proj4js because its definition was loaded in the html.
+// Note that we are getting the projection object here to set the extent. If
+// you do not need this, you do not have to use ol.proj.get(); simply use the
+// string code in the view projection below and the transforms will be
+// registered transparently.
 var projection = ol.proj.get('EPSG:21781');
 // The extent is used to determine zoom level 0. Recommended values for a
 // projection's validity extent can be found at http://epsg.io/.

examples/wms-no-proj.js

@@ -42,8 +42,10 @@ var layers = [
 ];
 
 // A minimal projection object is configured with only the SRS code and the map
-// units. No client side coordinate transforms are possible with such a
-// projection object.
+// units. No client-side coordinate transforms are possible with such a
+// projection object. Requesting tiles only needs the code together with a
+// tile grid of Cartesian coordinates; it does not matter how those
+// coordinates relate to latitude or longitude.
 var projection = new ol.proj.Projection({
   code: 'EPSG:21781',
   units: 'm'