diff --git a/ui (gen4)/features/history.js b/ui (gen4)/features/history.js
index 1c7c1dea..b5d06f9d 100755
--- a/ui (gen4)/features/history.js	
+++ b/ui (gen4)/features/history.js	
@@ -342,7 +342,7 @@ var URLHistoryLocalStorageActions = actions.Actions({
 		}
 	}],
 
-	saveURLHistory: ['History/',
+	storeURLHistory: ['History/',
 		function(){
 			var history = this.config['url-history-local-storage-key']
 			if(history != null){
@@ -350,9 +350,9 @@ var URLHistoryLocalStorageActions = actions.Actions({
 					JSON.stringify(this.url_history) 
 			}
 
-			this.saveLocation()
+			this.storeLocation()
 		}],
-	saveLocation: ['History/',
+	storeLocation: ['History/',
 		function(){
 			var loaded = this.config['url-history-loaded-local-storage-key']
 
@@ -404,16 +404,16 @@ module.URLHistoryLocalStorage = core.ImageGridFeatures.Feature({
 			function(){ this.loadLastSavedBasePath() }], 
 
 		['stop.pre',
-			function(){ this.saveURLHistory() }], 
+			function(){ this.storeURLHistory() }], 
 
 		// save base_path...
 		['load', 
-			function(){ this.location && this.location.path && this.saveLocation() }],
+			function(){ this.location && this.location.path && this.storeLocation() }],
 
 		// save...
 		['pushURLToHistory dropURLFromHistory setTopURLHistory', 
 			function(){ 
-				this.saveURLHistory()
+				this.storeURLHistory()
 			}],
 		// clear...
 		['clearURLHistory.pre',
@@ -465,7 +465,7 @@ module.URLHistoryFSWriter = core.ImageGridFeatures.Feature({
 						var e = that.url_history[l.path]
 						if(e != null){
 							e.open = l.method
-							that.saveURLHistory()
+							that.storeURLHistory()
 
 						} else {
 							that.pushURLToHistory(l.path, l.method)
diff --git a/ui (gen4)/features/location.js b/ui (gen4)/features/location.js
index d586f1b8..2616b716 100755
--- a/ui (gen4)/features/location.js	
+++ b/ui (gen4)/features/location.js	
@@ -97,8 +97,7 @@ var LocationActions = actions.Actions({
 	// NOTE: the method is needed to enable us to get the action return
 	// 		value...
 	set location(value){
-		this.loadLocation(value)
-	},
+		this.loadLocation(value) },
 
 
 	clearLoaction: ['File/Clear location',
@@ -178,74 +177,124 @@ var LocationActions = actions.Actions({
 			return res
 		}],
 
-	// XXX need a way to get save method...
-	// 		- rename .location.method to .location.load and add .location.save 
-	// 		- treat method as protocol and add a method registry API
-	// 			this is more flexible as we can add as many methods per
-	// 			protocol as we need and add a command action:
-	// 				- execute command in current protocol
-	// 					.locationCall("command", ...)
-	// 				- execute command in specific protocol
-	// 					.locationCall('protocol:command', ..)
-	// 				- show current protocol
-	// 					.locationCall("?")
-	// 				- list commands
-	// 					.locationCall("??")
-	// 					.locationCall('protocol:??')
-	// 			we can implicitly define protocols via action attrs:
-	// 				loadIndex: ['...',
-	// 					{locationProtocol: 'file:load'},
-	// 					function(){ ... }],
-	locationDispatch: ['- File/',
+	// XXX
+	// XXX should these have the same effect as .dispatch('location:*:load', location)???
+	// 		...another way to put it is should we call this from dispatch?
+	// 			...feels like yes -- this will turn into another Action-like
+	// 			protocol...
+	// 				...or we can use this to wrap the actual matching action...
+	_loadLocation: ['- File/Save location',
+		{protocol: 'location:*:load'},
+		function(location){
+			this.location.method = this.locationMethod(location)
+			this.dispatch('location:*:load', location) 
+		}],
+	_saveLocation: ['- File/Save location',
+		{protocol: 'location:*:save'},
+		function(location){
+			this.location.method = this.locationMethod(location)
+			this.dispatch('location:*:save', location) }],
+	_locationMethod: ['- File/',
+		{protocol: 'location:?'},
+		function(location){ 
+			return (location || this.location).method || null }],
+
+
+	// format:
+	// 	{
+	// 		'protocol:method': 'actionName',
+	//
+	// 		'family:protocol:method': 'actionName',
+	//
+	// 		'family:*': 'actionName',
+	// 		...
+	// 	}
+	get protocols(){
+		var cache = this.__location_protocol_cache = this.__location_protocol_cache 
+			|| this.cacheProtocols()
+		return cache
+	},
+	cacheProtocols: ['- File/',
+		function(){
+			var that = this
+			var res = {}
+			this.actions.forEach(function(n){
+				var proto = that.getActionAttr(n, 'protocol')
+				if(proto){
+					res[proto] = n
+				}
+			})
+			return res
+		}],
+	dispatch: ['- File/',
+		core.doc`
+
+			Execute command in specific protocol...
+			.dispatch('protocol:command', ..)
+			.dispatch('family:protocol:command', ..)
+				-> result
+
+			XXX defaults...
+
+			XXX introspection...
+		`,
 		function(spec){
-			spec = spec instanceof Array ? spec : spec.split(':')
 			var args = [].slice.call(arguments, 1)
+			spec = spec instanceof Array ? spec : spec.split(':')
 
-			var action = spec.pop()
-			var protocol = spec.shift() || this.location.method
+			var cache = this.protocols
+			var protocols = Object.keys(cache)
 
-			// format:
-			// 	{
-			// 		'protocol:method': 'actionName',
-			// 		...
-			// 	}
-			var cache = this.__location_protocol_cache = 
-				this.__location_protocol_cache || this.cacheLocationProtocols()
+			// get all matching paths...
+			var matches = protocols.slice()
+				.map(function(p){ return p.split(':') })
+			spec.forEach(function(e, i){
+				matches = matches
+					.filter(function(p){ return e == '*' || p[i] == e }) })
+			matches = matches
+				// remove matches ending with '*'... (XXX ???)
+				.filter(function(p){ return p.slice(-1)[0] != '*' })
+				.map(function(p){ return p.join(':') })
 
-			// get protocol...
-			if(action == '?'){
-				return protocol
+			// fill in the gaps...
+			var i = spec.indexOf('*')
+			while(spec.indexOf('*') >= 0){
+				var handler = cache[spec.slice(0, i).concat('?').join(':')]
+				if(handler){
+					spec[i] = this[handler].apply(this, args)
+					i = spec.indexOf('*')
 
-			// get available methods for protocol...
-			} else if(action == '??'){
-				return Object.keys(cache)
-					.filter(function(e){ return e.startsWith(protocol + ':') })
-					.map(function(e){ return e.split(':').pop() })
-			
-			// list all protocols...
-			} else if(protocol == '??' && action == '*'){
-				return Object.keys(cache)
-					.map(function(e){ return e.split(':').pop() })
-					.unique()
+				// error...
+				// XXX how do we break out of this???
+				} else {
+					throw ('No default defined for: '+ spec.slice(0, i+1).join(':'))
+				}
+			}
 
-			// list protocols implementing specific action...
-			} else if(protocol == '??'){
-				return Object.keys(cache)
-					.filter(function(e){ return e.endsWith(':'+ action) })
-					.map(function(e){ return e.split(':')[0] })
-					.unique()
+			// introspection...
+			// XXX this supports only one '??'
+			var i = spec.indexOf('??')
+			if(i >= 0){
+				var head = spec.slice(0, i).join(':')
+				var tail = spec.slice(i+1).join(':')
+				console.log(head, tail)
+				return protocols
+					.filter(function(p){
+						return p.startsWith(head) 
+							&& (tail == '' 
+								|| (p.endsWith(tail)
+									&& p.length > (head.length + tail.length + 2))) })
 
 			// call method...
 			} else {
-				// XXX args???
-				this[cache[protocol +':'+ action]].call(this)
+				var m = spec.join(':')
+				console.log('>>>', m)
+
+				// XXX take all the matches and chain call them...
+				return this[cache[m]].apply(this, args)
 			}
 		}],
-	saveLocation: ['- File/Save location',
-		function(location){
-			// XXX
-			this.locationDispatch('save')
-		}],
+
 })
 
 module.Location = core.ImageGridFeatures.Feature({
diff --git a/ui (gen4)/features/meta.js b/ui (gen4)/features/meta.js
index 2fde753f..16d9a0bc 100755
--- a/ui (gen4)/features/meta.js	
+++ b/ui (gen4)/features/meta.js	
@@ -64,6 +64,7 @@ core.ImageGridFeatures.Feature('viewer-testing', [
 
 	'ui-single-image',
 	//'ui-partial-ribbons',
+	// XXX this still has problems...
 	'ui-partial-ribbons-2',
 
 	'marks',
diff --git a/ui (gen4)/features/ui-partial-ribbons-2.js b/ui (gen4)/features/ui-partial-ribbons-2.js
index 65037875..205c8d65 100755
--- a/ui (gen4)/features/ui-partial-ribbons-2.js	
+++ b/ui (gen4)/features/ui-partial-ribbons-2.js	
@@ -35,7 +35,10 @@ var PartialRibbonsActions = actions.Actions({
 		// 	'resize'
 		'ribbons-in-place-update-mode': 'resize',
 
-		'ribbons-in-place-update-timeout': 200,
+		'ribbons-in-place-update-timeout': 100,
+
+		// XXX
+		'ribbon-update-timeout': 120,
 	},
 
 	updateRibbon: ['- Interface/Update partial ribbon size', 
@@ -63,6 +66,7 @@ var PartialRibbonsActions = actions.Actions({
 			var t = Date.now()
 			this.__last_ribbon_update = this.__last_ribbon_update || t
 			var timeout = this.config['ribbons-in-place-update-timeout']
+			var	update_timeout = this.config['ribbon-update-timeout']
 
 			// localize transition prevention... 
 			// NOTE: we can't get ribbon via target directly here as
@@ -93,8 +97,10 @@ var PartialRibbonsActions = actions.Actions({
 					// ribbon shorter than we expect...
 					|| (loaded < size && na + pa > loaded)
 					// ribbon too long...
-					|| loaded > size * threshold){
-				//console.log('RESIZE')
+					|| loaded > size * threshold
+					// passed hard threshold -- too close to edge...
+					|| (nl < w && na > nl) || (pl < w && pa > pl)){
+				//console.log('RESIZE (sync)')
 				this.resizeRibbon(target, size)
 
 			// more complex cases...
@@ -104,7 +110,7 @@ var PartialRibbonsActions = actions.Actions({
 					|| (pl < update_threshold && pa > pl) 
 					// loaded more than we need by threshold...
 					|| nl + pl + 1 > size + update_threshold){
-				// resize mode...
+				// resize...
 				if(this.config['ribbons-in-place-update-mode'] == 'resize'
 						// no ribbon loaded...
 						|| r.length == 0 
@@ -114,26 +120,36 @@ var PartialRibbonsActions = actions.Actions({
 						// full screen...
 						|| (this.toggleSingleImage 
 							&& this.toggleSingleImage('?') == 'on')){
-					//console.log('RESIZE', t-this.__last_ribbon_update)
-					this.resizeRibbon(target, size)
+					return function(){
+						var that = this
+						// sync update...
+						if(update_timeout == null){
+							//console.log('RESIZE (post)', t-this.__last_ribbon_update)
+							this.resizeRibbon(target, size)
+
+						// async update...
+						} else {
+							this.__update_timeout
+								&& clearTimeout(this.__update_timeout)
+							this.__update_timeout = setTimeout(function(){ 
+								//console.log('RESIZE (timeout)', t-this.__last_ribbon_update)
+								delete that.__update_timeout
+								that.resizeRibbon(target, size) 
+							}, update_timeout)
+						}
+					}
 
 				// in-place update...
 				// XXX this is faster than .resizeRibbon(..) but it's not
-				// 		used unconditionally because I can't get rid or
+				// 		used unconditionally because I can't get rid of
 				// 		sync up images being replaced...
 				// 		...note that .resizeRibbon(..) is substantially 
 				// 		slower (updates DOM), i.e. introduces a lag, but
 				// 		the results look OK...
-				//
-				// 		Approaches:
-				// 			- preloading a target section off-screen
-				// 				...results in two freezes instead of one
-				// 			- CSS will-change: background-image (???)
-				// 			- revise .updateImage(..)
-				//
-				// 		Q: can this be done within 1/60s???
-				// XXX one approach here might be:
-				// 		wait for images to preload and only then update...
+				// XXX approaches to try:
+				// 		- wait for images to preload and only then update...
+				// 		- preload images in part of a ribbon and when ready update...
+				// 			...this is like the first but we wait for less images...
 				} else {
 					//console.log('UPDATE', t - this.__last_ribbon_update)
 					var c = gids.indexOf(data.getImage('current', r_gid))
diff --git a/ui (gen4)/features/ui.js b/ui (gen4)/features/ui.js
index 6d11bdba..c4fb0094 100755
--- a/ui (gen4)/features/ui.js	
+++ b/ui (gen4)/features/ui.js	
@@ -1927,6 +1927,8 @@ var ControlActions = actions.Actions({
 		// if true and ribbon is panned off screen, the image will be 
 		// centered, else behave just like partially off screen...
 		'center-off-screen-paned-images': false,
+
+		'mouse-wheel-scale': 0.5,
 	},
 
 	// Image click events...
@@ -2386,6 +2388,112 @@ var ControlActions = actions.Actions({
 				}
 			})],
 
+	// XXX need:
+	// 		- prevent ribbon from scrolling off screen...
+	// 		- handle acceleration -- stop and update just before scrolling off the edge...
+	// 		- update...
+	// XXX might be a good idea to use the viewer instead of ribbons as source...
+	// 		...this will prevent losing control of the ribbon when it goes out
+	// 		from under the cursor...
+	// 		...detect via cursor within the vertical band of the ribbon...
+	toggleMouseWheelHandling: ['Interface/Mouse wheel handling',
+		toggler.Toggler(null,
+			function(){ 
+				return this.ribbons 
+					&& this.ribbons.viewer 
+					&& this.ribbons.viewer.hasClass('mouse-wheel-scroll') ?
+						'handling-mouse-wheel' 
+						: 'none' },
+			'handling-mouse-wheel',
+			function(state){
+				var that = this
+
+				/*
+				var focus_central = function(rgid){
+					// see if we need to change focus...
+					var current_ribbon = that.data.getRibbon()
+					if(current_ribbon == rgid){
+						var central = that.ribbons.getImageByPosition('center', r)
+						var gid = that.ribbons.getElemGID(central)
+						// silently focus central image...
+						if(that.config['focus-central-image'] == 'silent'){
+							that.data.focusImage(gid)
+							that.ribbons.focusImage(that.current)
+							
+						// focus central image in a normal manner...
+						} else if(that.config['focus-central-image']){
+							that.data.focusImage(gid)
+							that.focusImage()
+						}
+					}
+				}
+				*/
+
+				var setup = this.__wheel_handler_setup = this.__wheel_handler_setup 
+					|| function(_, target){
+						var that = this
+
+						var r = this.ribbons.getRibbon(target)
+						var rgid = this.ribbons.getElemGID(r)
+
+						// XXX vertical scroll...
+						this.ribbons.viewer
+							.on('wheel', function(){
+							})
+
+						// horizontal scroll...
+						r.on('wheel', function(){
+							event.preventDefault()
+
+							var s = that.config['mouse-wheel-scale'] || 1
+							var vmin = Math.min(document.body.offsetWidth, document.body.offsetHeight)
+							var left = parseFloat(($(this).transform('translate3d') || [0])[0])/100 * vmin
+
+							// XXX inertia problem -- it's too easy to scroll a ribbon off the screen...
+							// 		try:
+							// 			- limit speed
+							// 			- limit distance 
+							// 				1-2 screens -> stop for timeout before continue
+							// 				...need to keep track of "scroll sessions"
+
+							// XXX prevent scroll off screen....
+
+							// XXX prevent scroll off loaded edge...
+							
+							// XXX focus_central(rgid) when scroll slows down...
+							// 		(small deltaX or longer time between triggerings)...
+
+							// XXX do we need to do requestAnimationFrame(..) render...
+							// 		...see toggleRibbonPanHandling(..) for an implementation...
+
+							// do the actual move...
+							r.transform({
+								x: ((left - (event.deltaX * s)) / vmin * 100) + 'vmin',
+							})
+						})
+
+					}
+
+				// on...
+				if(state == 'on'){
+					this.ribbons.viewer.addClass('mouse-wheel-scroll')
+					// NOTE: we are resetting this to avoid multiple setting
+					// 		handlers...
+					this.off('updateRibbon', setup)
+					this.on('updateRibbon', setup)
+
+					this.data.ribbon_order.forEach(function(gid){
+						setup.call(that, null, gid) })
+
+				// off...
+				} else {
+					this.ribbons.viewer.removeClass('mouse-wheel-scroll')
+					this.off('updateRibbon', setup)
+
+					this.data.ribbon_order.forEach(function(gid){
+						that.ribbons.getRibbon(gid).off('wheel') })
+				}
+			})],
 	
 	togglePinchHandling: ['Interface/Pinch zoom handling',
 		function(){
diff --git a/ui (gen4)/index.html b/ui (gen4)/index.html
index 6bf41713..651e588a 100755
--- a/ui (gen4)/index.html	
+++ b/ui (gen4)/index.html	
@@ -58,7 +58,6 @@ if(window.require && window.nw){
 <script src="ext-lib/hammer.min.js"></script>
 <script src="ext-lib/jquery.hammer.js"></script>
 
-
 <script src="lib/jli.js"></script>
 
 <script data-main="ui" src="ext-lib/require.js"></script>
diff --git a/ui (gen4)/lib/transform.js b/ui (gen4)/lib/transform.js
index 2dff98d9..6d40ac66 100755
--- a/ui (gen4)/lib/transform.js	
+++ b/ui (gen4)/lib/transform.js	
@@ -299,7 +299,11 @@ var transformEditor = function(){
 
 			var aliases = Object.keys(spec)
 
-			var r = reduce == 'sum' ? function(a, b){ return a + b }
+			var r = reduce == 'sum' ? function(a, b){ 
+				return a == 0 ? b 
+					: b == 0 ? a
+					: a == 0 && b == 0 ? 0
+					: a + b }
 				: reduce == 'mul' ? function(a, b){ return a * b }
 				: reduce == 'last' ? function(a, b){ return b != null ? b : a }
 				: reduce