diff --git a/lib/jli.js b/lib/jli.js
index 626b1ba..a8f97d2 100755
--- a/lib/jli.js
+++ b/lib/jli.js
@@ -13,14 +13,14 @@
 
 /*********************************************************************/
 
-// this will create a function that will cycle through a class_list on elem 
+// This will create a function that will cycle through a class_list on elem 
 // calling the optional callbacks before and/or after.
-// if class_list is given as a string, then this will create a toggler that 
+// If class_list is given as a string, then this will create a toggler that 
 // will turn the given class on the element on and off.
 //
-// elem is a jquery compatible object; default use-case: a css selector.
+// Elem is a jquery compatible object; default use-case: a css selector.
 //
-// if class_list is a string, the resulting function understands the 
+// If class_list is a string, the resulting function understands the 
 // folowing arguments:
 // 	- <index>		: 0 for 'off' and 1 for 'on' (see below)
 // 	- 'on'			: switch mode on -- add class
@@ -28,7 +28,7 @@
 // 	- '?'			: return current state ('on'|'off')
 // 	- no arguments	: toggle the state
 //
-// otherwise, if class_list is a list of strings:
+// Otherwise, if class_list is a list of strings:
 //  - <index>		: explicitly set the state to index in class_list
 //  - <class-name>	: explicitly set a class from the list
 // 	- '?'			: return current state ('on'|'off')
@@ -45,6 +45,17 @@
 // 		to write the classes without leading dots, this now will normalize
 // 		the class list, so now this will correctly treat both dotted 
 // 		and non-dotted class names...
+//
+//
+// This also takes one or two callbacks. If only one is given then it is
+// called after (post) the change is made. If two are given then the first
+// is called before the change and the second after the change.
+// The callbacks are passed the current action.
+//
+// NOTE: the pre-callback will get the "intent" action, i.e. the state the
+// 		we are changing into but the changes are not yet made.
+// NOTE: if the pre-callback explicitly returns false, then the change will
+// 		not be made.
 function createCSSClassToggler(elem, class_list, callback_a, callback_b){
 	var bool_action = false
 	if(typeof(class_list) == typeof('')){
@@ -55,8 +66,8 @@ function createCSSClassToggler(elem, class_list, callback_a, callback_b){
 	// NOTE: this is here because I've made the error of including a 
 	// 		leading "." almost every time I use this after I forget 
 	// 		the UI...
-	class_list = $(class_list).map(function(i, e){
-		return $(e.split(' ')).map(function(i, c){
+	class_list = $(class_list).map(function(_, e){
+		return $(e.split(' ')).map(function(_, c){
 			c = c.trim()
 			return c[0] == '.' ? c.slice(1) : c
 		}).toArray().join(' ')
@@ -122,8 +133,11 @@ function createCSSClassToggler(elem, class_list, callback_a, callback_b){
 		}
 
 		// pre callback...
-		if(callback_a != null){
-			callback_a(action)
+		if(callback_pre != null){
+			var res = callback_pre(action)
+			if(res === false){
+				return
+			}
 		}
 		// update the element...
 		elem.removeClass(class_list.join(' '))
@@ -131,8 +145,8 @@ function createCSSClassToggler(elem, class_list, callback_a, callback_b){
 			elem.addClass(cls)
 		}
 		// post callback...
-		if(callback_b != null){
-			callback_b(action)
+		if(callback_post != null){
+			callback_post(action)
 		}
 
 		return action
diff --git a/magazine.js b/magazine.js
index 634b8bf..ad9c3ae 100755
--- a/magazine.js
+++ b/magazine.js
@@ -93,7 +93,6 @@ var _PAGE_VIEW
 var togglePageView = createCSSClassToggler(
 	'.viewer', 
 	'page-view-mode',
-	null,
 	// post-change callback...
 	function(action){
 		if(action == 'on'){