How does OpenLayers determine a layer's projection?

Question

Could anyone explain the strategy OpenLayers take to determine the layer's projection?

For example, if I didn't explicitly specify any projection for a marker layer, what projection would the layer take?

Answer 1

If you don't specify a projection the projection will be null (undefined) - when the layer is added to the map it will inherit the map's projection.

This is easily verified with the following code:

aLayer = new OpenLayers.Layer.Markers();
alert("Projection : " + aLayer.projection);     // Projection: null
map.addLayer(aLayer);
alert("Projection after adding to map: " + aLayer.projection);  // Projection: EPSG: 900913