diff --git a/ui (gen4)/ui.js b/ui (gen4)/ui.js
index 7e3cfb73..fff1cfd5 100755
--- a/ui (gen4)/ui.js	
+++ b/ui (gen4)/ui.js	
@@ -215,6 +215,7 @@ $(function(){
 		'ui-partial-ribbons',
 		'ui-ribbon-align-to-order',
 		'ui-single-image-view',
+		'fs-loader',
 
 		// ui elements...
 		'image-marks',
diff --git a/ui (gen4)/viewer.js b/ui (gen4)/viewer.js
index f5d3aa3a..c5eae256 100755
--- a/ui (gen4)/viewer.js	
+++ b/ui (gen4)/viewer.js	
@@ -1185,6 +1185,10 @@ var FeatureProto =
 module.FeatureProto = {
 	tag: null,
 
+	isApplicable: function(actions){
+		return true
+	},
+
 	getPriority: function(){
 		var res = this.priority || 0
 		return res == 'high' ? 99
@@ -1282,10 +1286,9 @@ Feature.prototype.constructor = Feature
 // XXX if this works out might be a good idea to organize everything as
 // 		a feature... including the Client and Viewer
 // 		...needs more thought...
-// XXX add a standard doc set...
 var FeatureSet =
 module.FeatureSet = {
-	buildFeatureList: function(lst){
+	buildFeatureList: function(obj, lst){
 		lst = lst.constructor !== Array ? [lst] : lst
 
 		var that = this
@@ -1298,12 +1301,25 @@ module.FeatureSet = {
 		})
 
 		// sort features via dependencies...
+		var unapplicable = []
 		var conflicts = {}
 		lst = lst.filter(function(n, i){
 			var e = that[n]
-			if(e == null || e.depends == null ){
+			if(e == null){
 				return true
 			}
+
+			// check applicability...
+			if(!e.isApplicable(obj)){
+				unapplicable.push(n)
+				return false
+			}
+
+			// no dependencies...
+			if(e.depends == null ){
+				return true
+			}
+
 			// keep only conflicting...
 			var deps = e.depends.filter(function(dep){
 				dep = lst.indexOf(dep)
@@ -1350,13 +1366,14 @@ module.FeatureSet = {
 		return {
 			features: lst,
 			excluded: excluded,
-			conflicts: conflicts
+			conflicts: conflicts,
+			unapplicable: unapplicable,
 		}
 	},
 
 	setup: function(obj, lst){
 		lst = lst.constructor !== Array ? [lst] : lst
-		var features = this.buildFeatureList(lst)
+		var features = this.buildFeatureList(obj, lst)
 		lst = features.features
 
 		// check for conflicts...
@@ -1377,6 +1394,12 @@ module.FeatureSet = {
 					features.excluded.join(', '))
 		}
 
+		// report unapplicable features...
+		if(features.unapplicable.length > 0){
+			console.log('Features not applicable in current context:', 
+					features.unapplicable.join(', '))
+		}
+
 		// do the setup...
 		var that = this
 		var setup = FeatureProto.setup
@@ -2434,6 +2457,21 @@ module.ImageBookmarks = Feature({
 
 
 
+//---------------------------------------------------------------------
+var FileSystemLoader = 
+module.FileSystemLoader = Feature({
+	title: '',
+	doc: '',
+
+	tag: 'fs-loader',
+
+	isApplicable: function(){
+		return window.nodejs != null
+	},
+})
+
+
+
 
 /**********************************************************************
 * vim:set ts=4 sw=4 :                                                */