diff --git a/API-&-Defaults-Discussion.md b/API-&-Defaults-Discussion.md
index 330b064..3121a45 100644
--- a/API-&-Defaults-Discussion.md
+++ b/API-&-Defaults-Discussion.md
@@ -1,5 +1,7 @@
 OpenLayers 3 should provide an API that makes it easy to accomplish common use cases. People who do not need to leverage the full functionality should be provided fast lanes for a leaner and easy to use configuration. Defaults should be set in the right places to avoid duplicated code.
 
+This document is work in progress. At the time of writing, it reflects @ahocevar's thoughts on a few aspects of the library that come to mind when thinking about API and defaults.
+
 ## Map with WMS layer (tiled) in default projection (EPSG:3857)
 
     new ol.Map({
@@ -23,7 +25,6 @@ OpenLayers 3 should provide an API that makes it easy to accomplish common use c
 
     new ol.Map({
         layers: [
-            // suitable layer type can be chosen based on the source
             new ol.source.TiledWMS({
                 url: '/geoserver/wms',
                 params: {
@@ -31,10 +32,11 @@ OpenLayers 3 should provide an API that makes it easy to accomplish common use c
                 }
             })
         ],
-        // would be even nicer to provide center and zoom as direct map config options
         view: {
             projection: {
                 code: 'EPSG:31256',
+                units: 'meters',
+                // validity extent from http://spatialreference.org/
                 extent: [-115317.3972, 151511.8020, 64307.1064, 432456.2246]
             },
             center: [47, 15],
@@ -42,4 +44,44 @@ OpenLayers 3 should provide an API that makes it easy to accomplish common use c
         }
     });
 
-The layer source should not need a projection configuration - it should get it from the view. With the projection's extent, the layer source should be able to create a default tile grid.
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+The layer source should not need a projection configuration - it should get it from the view. With the projection's extent, the layer source should be able to create a default tile grid. The map's zoom levels will be derived from the projection's extent as well.
+
+## Map with custom projection and single image WMS layer
+
+Exactly the same as above, only with `ol.source.SingleImageWMS` instead of `ol.Source.TiledWMS`. It should not be necessary to configure the layer source with a resolutions array, and a single image source should be able to serve any resolution that the map uses.
+
+## Map with custom projection, WMS layer with custom tile grid
+
+
+    new ol.Map({
+        layers: [
+            new ol.source.TiledWMS({
+                url: '/geoserver/wms',
+                params: {
+                   'LAYERS': 'usa:states' // would be nice without quotes for the key
+                },
+                tileGrid: {
+                    maxExtent: [-100000, 160000, 60000, 430000],
+                    resolutions: [1000, 500, 200, 100, 50, 20, 10, 5, 2, 1]
+                }
+            })
+        ],
+        view: {
+            projection: {
+                code: 'EPSG:31256',
+                units: 'meters',
+                // validity extent from http://spatialreference.org/
+                extent: [-115317.3972, 151511.8020, 64307.1064, 432456.2246]
+            },
+            center: [47, 15],
+            zoom: 3
+        }
+    });
+
+Since the TileGrid is a very complex thing, and most use cases except ArcGISCache and WMTS use the same grid extent for each resolution, it makes sense to provide a convenience configuration with a common maxExtent and a set of resolutions.
+
+## Thoughts on defaults
+
+Looking at the current code, there are still more than one places with Web Mercator related defaults. The central place for projection related defaults should be the `ol.projection` package. If layer sources can lazily create a TileGrid upon rendering, it will be possible to use map defaults for layer sources.
+
+The concept of user projections works best in the context of a map. Classes like Coordinate or Extent do not necessarily need to know about the user projection if the map (or the view) provides extent and center related getters.
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