Use the source, Luke!

Code:
CL_CollisionOutline::CL_CollisionOutline(const CL_StringRef &resource_id, CL_ResourceManager *manager)
{
	resource = manager->get_resource(resource_id);
	if (resource.get_type() != "collisionoutline")
		throw CL_Exception(cl_format("Resource '%1' is not of type 'collisionoutline'", resource_id));
so, first thing we notice is that the resource type has to be collisionoutline.

Code:
	data = CL_SharedPtr<CL_ResourceData_CollisionOutline>(new CL_ResourceData_CollisionOutline(resource));
secondly, the rest of the interesting code is separated into a class called CL_ResourceData_CollisionOutline.

Code:
CL_ResourceData_CollisionOutline::CL_ResourceData_CollisionOutline(CL_Resource &resource)
{
	CL_String filename = resource.get_element().get_attribute("file");
	int alpha_limit = CL_StringHelp::text_to_int( (resource.get_element().get_attribute("alpha_value", "128")));
	CL_String accuracy_str = resource.get_element().get_attribute("accuracy", "medium");
	CL_OutlineAccuracy accuracy;

	if(accuracy_str == "high")
		accuracy = accuracy_high;
	else if(accuracy_str == "medium")
		accuracy = accuracy_medium;
	else if(accuracy_str == "low")
		accuracy = accuracy_low;
	else if(accuracy_str == "poor")
		accuracy = accuracy_poor;
    else
		accuracy = accuracy_raw;

	CL_CollisionOutline_Generic *outline;

	if (filename.length() >= 3 && filename.substr(filename.length()-3, 3) == "out" )
	{
		outline = new CL_CollisionOutline_Generic(
			new CL_OutlineProviderFile(filename, resource.get_manager().get_directory(resource)), accuracy_raw);
	}
	else
	{
		CL_PixelBuffer pbuf = CL_ImageProviderFactory::load(filename, resource.get_manager().get_directory(resource), "");
		outline = new CL_CollisionOutline_Generic(
			new CL_OutlineProviderBitmap(pbuf, alpha_limit), accuracy );
	}

	CL_CollisionOutline *collision_outline_tmp = 
		new CL_CollisionOutline(outline->contours, outline->width, outline->height);
 
....
}
We can now easily read what kind of structure it expects from the xml:

file = filename, which can be a .out file, or an image.
alpha_limit = alpha limit used for extracting if its an image.
accuracy = high, medium, low, poor or raw accuracy if its an image.


Examples:
<collisionoutline file="mysprite.col"/>
<collisionoutline file="mysprite.png" accuracy="medium" alpha_limit="128"/>