define(["./sniff", "./_base/window"],
		function(has, win){
	// module:
	//		dojo/dom

	// FIXME: need to add unit tests for all the semi-public methods

	if(has("ie") <= 7){
		try{
			document.execCommand("BackgroundImageCache", false, true);
		}catch(e){
			// sane browsers don't have cache "issues"
		}
	}

	// =============================
	// DOM Functions
	// =============================

	// the result object
	var dom = {
		// summary:
		//		This module defines the core dojo DOM API.
	};

	if(has("ie")){
		dom.byId = function(id, doc){
			if(typeof id != "string"){
				return id;
			}
			var _d = doc || win.doc, te = id && _d.getElementById(id);
			// attributes.id.value is better than just id in case the
			// user has a name=id inside a form
			if(te && (te.attributes.id.value == id || te.id == id)){
				return te;
			}else{
				var eles = _d.all[id];
				if(!eles || eles.nodeName){
					eles = [eles];
				}
				// if more than 1, choose first with the correct id
				var i = 0;
				while((te = eles[i++])){
					if((te.attributes && te.attributes.id && te.attributes.id.value == id) || te.id == id){
						return te;
					}
				}
			}
		};
	}else{
		dom.byId = function(id, doc){
			// inline'd type check.
			// be sure to return null per documentation, to match IE branch.
			return ((typeof id == "string") ? (doc || win.doc).getElementById(id) : id) || null; // DOMNode
		};
	}
	/*=====
	 dom.byId = function(id, doc){
		 // summary:
		 //		Returns DOM node with matching `id` attribute or falsy value (ex: null or undefined)
		 //		if not found.  If `id` is a DomNode, this function is a no-op.
		 //
		 // id: String|DOMNode
		 //		A string to match an HTML id attribute or a reference to a DOM Node
		 //
		 // doc: Document?
		 //		Document to work in. Defaults to the current value of
		 //		dojo.doc.  Can be used to retrieve
		 //		node references from other documents.
		 //
		 // example:
		 //		Look up a node by ID:
		 //	|	var n = dojo.byId("foo");
		 //
		 // example:
		 //		Check if a node exists, and use it.
		 //	|	var n = dojo.byId("bar");
		 //	|	if(n){ doStuff() ... }
		 //
		 // example:
		 //		Allow string or DomNode references to be passed to a custom function:
		 //	|	var foo = function(nodeOrId){
		 //	|		nodeOrId = dojo.byId(nodeOrId);
		 //	|		// ... more stuff
		 //	|	}
	 };
	 =====*/

	dom.isDescendant = function(/*DOMNode|String*/ node, /*DOMNode|String*/ ancestor){
		// summary:
		//		Returns true if node is a descendant of ancestor
		// node: DOMNode|String
		//		string id or node reference to test
		// ancestor: DOMNode|String
		//		string id or node reference of potential parent to test against
		//
		// example:
		//		Test is node id="bar" is a descendant of node id="foo"
		//	|	if(dojo.isDescendant("bar", "foo")){ ... }

		try{
			node = dom.byId(node);
			ancestor = dom.byId(ancestor);
			while(node){
				if(node == ancestor){
					return true; // Boolean
				}
				node = node.parentNode;
			}
		}catch(e){ /* squelch, return false */ }
		return false; // Boolean
	};


	// TODO: do we need setSelectable in the base?

	// Add feature test for user-select CSS property
	// (currently known to work in all but IE < 10 and Opera)
	has.add("css-user-select", function(global, doc, element){
		// Avoid exception when dom.js is loaded in non-browser environments
		if(!element){ return false; }
		
		var style = element.style;
		var prefixes = ["Khtml", "O", "ms", "Moz", "Webkit"],
			i = prefixes.length,
			name = "userSelect",
			prefix;

		// Iterate prefixes from most to least likely
		do{
			if(typeof style[name] !== "undefined"){
				// Supported; return property name
				return name;
			}
		}while(i-- && (name = prefixes[i] + "UserSelect"));

		// Not supported if we didn't return before now
		return false;
	});

	/*=====
	dom.setSelectable = function(node, selectable){
		// summary:
		//		Enable or disable selection on a node
		// node: DOMNode|String
		//		id or reference to node
		// selectable: Boolean
		//		state to put the node in. false indicates unselectable, true
		//		allows selection.
		// example:
		//		Make the node id="bar" unselectable
		//	|	dojo.setSelectable("bar");
		// example:
		//		Make the node id="bar" selectable
		//	|	dojo.setSelectable("bar", true);
	};
	=====*/

	var cssUserSelect = has("css-user-select");
	dom.setSelectable = cssUserSelect ? function(node, selectable){
		// css-user-select returns a (possibly vendor-prefixed) CSS property name
		dom.byId(node).style[cssUserSelect] = selectable ? "" : "none";
	} : function(node, selectable){
		node = dom.byId(node);

		// (IE < 10 / Opera) Fall back to setting/removing the
		// unselectable attribute on the element and all its children
		var nodes = node.getElementsByTagName("*"),
			i = nodes.length;

		if(selectable){
			node.removeAttribute("unselectable");
			while(i--){
				nodes[i].removeAttribute("unselectable");
			}
		}else{
			node.setAttribute("unselectable", "on");
			while(i--){
				nodes[i].setAttribute("unselectable", "on");
			}
		}
	};

	return dom;
});