diff --git a/core/modules/background-actions.js b/core/modules/background-actions.js
new file mode 100644
index 000000000..95b4a611e
--- /dev/null
+++ b/core/modules/background-actions.js
@@ -0,0 +1,117 @@
+/*\
+title: $:/core/modules/background-actions.js
+type: application/javascript
+module-type: global
+
+Class to dispatch actions when filters change
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+function BackgroundActionDispatcher(filterTracker,wiki) {
+	var self = this;
+	this.filterTracker = filterTracker;
+	this.wiki = wiki;
+	this.nextTrackedFilterId = 1;
+	this.trackedFilters = Object.create(null); // Hashmap by id
+	// Track the filter for the background actions
+	this.filterTracker.track({
+		filterString: "[all[tiddlers+shadows]tag[$:/tags/BackgroundAction]!is[draft]]",
+		fnEnter: function fnEnter(title) {
+			return self.trackFilter(title);
+		},
+		fnLeave: function fnLeave(title,enterValue) {
+			self.untrackFilter(enterValue);
+		},
+		fnChange: function fnChange(title,enterValue) {
+			self.untrackFilter(enterValue);
+			return self.trackFilter(title);
+		},
+		fnProcess: function fnProcess(changes) {
+			self.process(changes);
+		}
+	});
+}
+
+BackgroundActionDispatcher.prototype.trackFilter = function(title) {
+	var tiddler = this.wiki.getTiddler(title),
+		id = this.nextTrackedFilterId++,
+		tracker = new BackgroundActionTracker({
+			wiki: this.wiki,
+			title: title,
+			trackFilter: tiddler.fields["track-filter"],
+			actions: tiddler.fields.text
+		});
+	this.trackedFilters[id] = tracker;
+	return id;
+};
+
+BackgroundActionDispatcher.prototype.untrackFilter = function(enterValue) {
+	var tracker = this.trackedFilters[enterValue];
+	if(tracker) {
+		tracker.destroy();
+	}
+	delete this.trackedFilters[enterValue];
+};
+
+BackgroundActionDispatcher.prototype.process = function(changes) {
+	for(var id in this.trackedFilters) {
+		this.trackedFilters[id].process(changes);
+	}
+};
+
+/*
+Represents an individual tracked filter. Options include:
+wiki: wiki to use
+title: title of the tiddler being tracked
+trackFilter: filter string to track changes
+actions: actions to be executed when the filter changes
+*/
+function BackgroundActionTracker(options) {
+	var self = this;
+	this.wiki = options.wiki;
+	this.title = options.title;
+	this.trackFilter = options.trackFilter;
+	this.actions = options.actions
+	this.filterTracker = new $tw.FilterTracker(this.wiki);
+	this.hasChanged = false;
+	this.trackerID = this.filterTracker.track({
+		filterString: this.trackFilter,
+		fnEnter: function(title) {
+			self.hasChanged = true;
+		},
+		fnLeave: function(title,enterValue) {
+			self.hasChanged = true;
+		},
+		fnProcess: function(changes) {
+			if(self.hasChanged) {
+				self.hasChanged = false;
+				self.wiki.invokeActionString(
+					self.actions,
+					null,
+					{
+						title: self.title
+					},{
+						parentWidget: $tw.rootWidget
+					}
+				);
+			}
+		}
+	});
+}
+
+BackgroundActionTracker.prototype.process = function(changes) {
+	this.filterTracker.handleChangeEvent(changes);
+};
+
+BackgroundActionTracker.prototype.destroy = function() {
+	this.filterTracker.untrack(this.trackerID);
+};
+
+exports.BackgroundActionDispatcher = BackgroundActionDispatcher;
+
+})();
diff --git a/core/modules/filter-tracker.js b/core/modules/filter-tracker.js
new file mode 100644
index 000000000..36744b2cf
--- /dev/null
+++ b/core/modules/filter-tracker.js
@@ -0,0 +1,108 @@
+/*\
+title: $:/core/modules/filter-tracker.js
+type: application/javascript
+module-type: global
+
+Class to track the results of a filter string
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+function FilterTracker(wiki) {
+	this.wiki = wiki;
+	this.trackers = [];
+	this.nextTrackerId = 1;
+}
+
+FilterTracker.prototype.handleChangeEvent = function(changes) {
+	this.processTrackers();
+	this.processChanges(changes);
+};
+
+/*
+Add a tracker to the filter tracker. Returns null if any of the parameters are invalid, or a tracker id if the tracker was added successfully. Options include:
+filterString: the filter string to track
+fnEnter: function to call when a title enters the filter results. Called even if the tiddler does not actually exist. Called as (title), and should return a truthy value that is stored in the tracker as the "enterValue"
+fnLeave: function to call when a title leaves the filter results. Called as (title,enterValue)
+fnChange: function to call when a tiddler changes in the filter results. Only called for filter results that identify a tiddler or shadow tiddler. Called as (title,enterValue), and may optionally return a replacement enterValue
+fnProcess: function to call each time the tracker is processed, after any enter, leave or change functions are called. Called as (changes)
+*/
+FilterTracker.prototype.track = function(options) {
+	// Add the tracker details
+	var tracker = {
+		id: this.nextTrackerId++,
+		filterString: options.filterString,
+		fnEnter: options.fnEnter,
+		fnLeave: options.fnLeave,
+		fnChange: options.fnChange,
+		fnProcess: options.fnProcess,
+		previousResults: [], // Results from the previous time the tracker was processed
+		resultValues: {} // Map by title to the value returned by fnEnter
+	};
+	this.trackers.push(tracker);
+	// Process the tracker
+	this.processTracker(this.trackers.length - 1);
+	return tracker.id;
+};
+
+FilterTracker.prototype.untrack = function(id) {
+	for(var t=0; t<this.trackers.length; t++) {
+		if(this.trackers[t].id === id) {
+			this.trackers.splice(t,1);
+			break;
+		}
+	}
+};
+
+FilterTracker.prototype.processTrackers = function() {
+	for(var t=0; t<this.trackers.length; t++) {
+		this.processTracker(t);
+	}
+};
+
+FilterTracker.prototype.processTracker = function(index) {
+	var tracker = this.trackers[index];
+	var results = [];
+	// Evaluate the filter and remove duplicate results
+	$tw.utils.each(this.wiki.filterTiddlers(tracker.filterString),function(title) {
+		$tw.utils.pushTop(results,title);
+	});
+	// Process the newly entered results
+	$tw.utils.each(results,function(title) {
+		if(tracker.previousResults.indexOf(title) === -1 && !tracker.resultValues[title] && tracker.fnEnter) {
+			tracker.resultValues[title] = tracker.fnEnter(title) || true;
+		}
+	});
+	// Process the results that have just left
+	$tw.utils.each(tracker.previousResults,function(title) {
+		if(results.indexOf(title) === -1 && tracker.resultValues[title] && tracker.fnLeave) {
+			tracker.fnLeave(title,tracker.resultValues[title]);
+			delete tracker.resultValues[title];
+		}
+	});
+	// Update the previous results
+	tracker.previousResults = results;
+};
+
+FilterTracker.prototype.processChanges = function(changes) {
+	for(var t=0; t<this.trackers.length; t++) {
+		var tracker = this.trackers[t];
+		$tw.utils.each(changes,function(change,title) {
+			if(title && tracker.previousResults.indexOf(title) !== -1 && tracker.fnChange) {
+				// Call the change function and if it doesn't return a value then keep the old value
+				tracker.resultValues[title] = tracker.fnChange(title,tracker.resultValues[title]) || tracker.resultValues[title];
+			}
+		});
+		if(tracker.fnProcess) {
+			tracker.fnProcess(changes);
+		}
+	}
+};
+
+exports.FilterTracker = FilterTracker;
+
+})();
diff --git a/core/modules/info/mediaquerytracker.js b/core/modules/info/mediaquerytracker.js
new file mode 100644
index 000000000..fdb1bc0f0
--- /dev/null
+++ b/core/modules/info/mediaquerytracker.js
@@ -0,0 +1,72 @@
+/*\
+title: $:/core/modules/info/mediaquerytracker.js
+type: application/javascript
+module-type: info
+
+Initialise $:/info/ tiddlers derived from media queries via 
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+exports.getInfoTiddlerFields = function(updateInfoTiddlersCallback) {
+	if($tw.browser) {
+		// Functions to start and stop tracking a particular media query tracker tiddler
+		function track(title) {
+			var result = {},
+				tiddler = $tw.wiki.getTiddler(title);
+			if(tiddler) {
+				var mediaQuery = tiddler.fields["media-query"],
+					infoTiddler = tiddler.fields["info-tiddler"],
+					infoTiddlerAlt = tiddler.fields["info-tiddler-alt"];
+				if(mediaQuery && infoTiddler) {
+					// Evaluate and track the media query
+					result.mqList = window.matchMedia(mediaQuery);
+					function getResultTiddlers() {
+						var value = result.mqList.matches ? "yes" : "no",
+							tiddlers = [];
+						tiddlers.push({title: infoTiddler, text: value});
+						if(infoTiddlerAlt) {
+							tiddlers.push({title: infoTiddlerAlt, text: value})
+						}
+						return tiddlers;
+					};
+					updateInfoTiddlersCallback(getResultTiddlers());
+					result.handler = function(event) {
+						updateInfoTiddlersCallback(getResultTiddlers());
+					};
+					result.mqList.addEventListener("change",result.handler);
+				}
+			}
+			return result;
+		}
+		function untrack(enterValue) {
+			if(enterValue.mqList && enterValue.handler) {
+				enterValue.mqList.removeEventListener("change",enterValue.handler);
+			}
+		}
+		// Track media query tracker tiddlers
+		function fnEnter(title) {
+			return track(title);
+		}
+		function fnLeave(title,enterValue) {
+			untrack(enterValue);
+		}
+		function fnChange(title,enterValue) {
+			untrack(enterValue);
+			return track(title);
+		}
+		$tw.filterTracker.track({
+			filterString: "[all[tiddlers+shadows]tag[$:/tags/MediaQueryTracker]!is[draft]]",
+			fnEnter: fnEnter,
+			fnLeave: fnLeave,
+			fnChange: fnChange
+		});
+	}
+	return [];
+};
+
+})();
diff --git a/core/modules/info/platform.js b/core/modules/info/platform.js
index 0eb0b9ea8..5021610f4 100644
--- a/core/modules/info/platform.js
+++ b/core/modules/info/platform.js
@@ -36,13 +36,6 @@ exports.getInfoTiddlerFields = function(updateInfoTiddlersCallback) {
 		// Screen size
 		infoTiddlerFields.push({title: "$:/info/browser/screen/width", text: window.screen.width.toString()});
 		infoTiddlerFields.push({title: "$:/info/browser/screen/height", text: window.screen.height.toString()});
- 		// Dark mode through event listener on MediaQueryList
- 		var mqList = window.matchMedia("(prefers-color-scheme: dark)"),
- 			getDarkModeTiddler = function() {return {title: "$:/info/darkmode", text: mqList.matches ? "yes" : "no"};};
- 		infoTiddlerFields.push(getDarkModeTiddler());
- 		mqList.addListener(function(event) {
- 			updateInfoTiddlersCallback([getDarkModeTiddler()]);
- 		});
 		// Language
 		infoTiddlerFields.push({title: "$:/info/browser/language", text: navigator.language || ""});
 	}
diff --git a/core/modules/startup/load-modules.js b/core/modules/startup/load-modules.js
index 1dc71f7ac..deb6493c6 100644
--- a/core/modules/startup/load-modules.js
+++ b/core/modules/startup/load-modules.js
@@ -16,6 +16,9 @@ Load core modules
 exports.name = "load-modules";
 exports.synchronous = true;
 
+// Set to `true` to enable performance instrumentation
+var PERFORMANCE_INSTRUMENTATION_CONFIG_TITLE = "$:/config/Performance/Instrumentation";
+
 exports.startup = function() {
 	// Load modules
 	$tw.modules.applyMethods("utils",$tw.utils);
@@ -35,6 +38,19 @@ exports.startup = function() {
 	$tw.macros = $tw.modules.getModulesByTypeAsHashmap("macro");
 	$tw.wiki.initParsers();
 	$tw.Commander.initCommands();
+	// --------------------------
+	// The rest of the startup process here is not strictly to do with loading modules, but are needed before other startup
+	// modules are executed. It is easier to put them here than to introduce a new startup module
+	// --------------------------
+	// Set up the performance framework
+	$tw.perf = new $tw.Performance($tw.wiki.getTiddlerText(PERFORMANCE_INSTRUMENTATION_CONFIG_TITLE,"no") === "yes");
+	// Kick off the filter tracker
+	$tw.filterTracker = new $tw.FilterTracker($tw.wiki);
+	$tw.wiki.addEventListener("change",function(changes) {
+		$tw.filterTracker.handleChangeEvent(changes);
+	});
+	// Kick off the background action dispatcher
+	$tw.backgroundActionDispatcher = new $tw.BackgroundActionDispatcher($tw.filterTracker,$tw.wiki);
 };
 
 })();
diff --git a/core/modules/startup/startup.js b/core/modules/startup/startup.js
index b971e473b..9092c5026 100755
--- a/core/modules/startup/startup.js
+++ b/core/modules/startup/startup.js
@@ -17,9 +17,6 @@ exports.name = "startup";
 exports.after = ["load-modules"];
 exports.synchronous = true;
 
-// Set to `true` to enable performance instrumentation
-var PERFORMANCE_INSTRUMENTATION_CONFIG_TITLE = "$:/config/Performance/Instrumentation";
-
 var widget = require("$:/core/modules/widgets/widget.js");
 
 exports.startup = function() {
@@ -57,8 +54,6 @@ exports.startup = function() {
 	}
 	// Initialise version
 	$tw.version = $tw.utils.extractVersionInfo();
-	// Set up the performance framework
-	$tw.perf = new $tw.Performance($tw.wiki.getTiddlerText(PERFORMANCE_INSTRUMENTATION_CONFIG_TITLE,"no") === "yes");
 	// Create a root widget for attaching event handlers. By using it as the parentWidget for another widget tree, one can reuse the event handlers
 	$tw.rootWidget = new widget.widget({
 		type: "widget",
diff --git a/core/wiki/SampleBackgroundAction Dark Mode.tid b/core/wiki/SampleBackgroundAction Dark Mode.tid
new file mode 100644
index 000000000..7bf07fef2
--- /dev/null
+++ b/core/wiki/SampleBackgroundAction Dark Mode.tid	
@@ -0,0 +1,9 @@
+title: SampleBackgroundAction: Dark Mode
+tags: $:/tags/BackgroundAction
+track-filter: [{$:/info/browser/darkmode}]
+
+<%if [{$:/info/browser/darkmode}match[no]] %>
+<$action-setfield $tiddler="$:/palette" text="$:/palettes/TwentyTwenties"/>
+<%else%>
+<$action-setfield $tiddler="$:/palette" text="$:/palettes/TwentyTwenties/Dark"/>
+<%endif%>
\ No newline at end of file
diff --git a/core/wiki/SampleBackgroundAction Story Change.tid b/core/wiki/SampleBackgroundAction Story Change.tid
new file mode 100644
index 000000000..6066650b4
--- /dev/null
+++ b/core/wiki/SampleBackgroundAction Story Change.tid	
@@ -0,0 +1,15 @@
+title: SampleBackgroundAction: Story Change
+tags: $:/tags/BackgroundAction
+track-filter: [list[$:/StoryList]]
+
+<$action-sendmessage $message="tm-notify" $param="SampleBackgroundAction: Story Change" list={{$:/StoryList!!list}}/>
+
+Story List:
+
+<ol>
+<$list filter="[enlist<list>]">
+<li>
+<$text text=<<currentTiddler>>/>
+</li>
+</$list>
+</ol>
diff --git a/core/wiki/config/MediaQueryTrackers/DarkLightPreferred.tid b/core/wiki/config/MediaQueryTrackers/DarkLightPreferred.tid
new file mode 100644
index 000000000..6b5e9f26c
--- /dev/null
+++ b/core/wiki/config/MediaQueryTrackers/DarkLightPreferred.tid
@@ -0,0 +1,5 @@
+title: $:/core/wiki/config/MediaQueryTrackers/DarkLightPreferred
+tags: $:/tags/MediaQueryTracker
+media-query: (prefers-color-scheme: dark)
+info-tiddler: $:/info/browser/darkmode
+info-tiddler-alt: $:/info/darkmode
diff --git a/editions/tw5.com/tiddlers/mechanisms/InfoMechanism.tid b/editions/tw5.com/tiddlers/mechanisms/InfoMechanism.tid
index 040dd7bd2..1cfeebb6e 100644
--- a/editions/tw5.com/tiddlers/mechanisms/InfoMechanism.tid
+++ b/editions/tw5.com/tiddlers/mechanisms/InfoMechanism.tid
@@ -4,8 +4,8 @@ tags: Mechanisms
 title: InfoMechanism
 type: text/vnd.tiddlywiki
 
-\define example(name)
-<$transclude tiddler="""$:/info/url/$name$""" mode="inline"/>
+\procedure example(name)
+<$text text={{{ [[$:/info/url/]addsuffix<name>get[text]] }}} />
 \end
 
 System tiddlers in the namespace `$:/info/` are used to expose information about the system (including the current browser) so that WikiText applications can adapt themselves to available features.
@@ -19,6 +19,8 @@ System tiddlers in the namespace `$:/info/` are used to expose information about
 |[[$:/info/browser/language]] |<<.from-version "5.1.20">> Language as reported by browser (note that some browsers report two character codes such as `en` while others report full codes such as `en-GB`) |
 |[[$:/info/browser/screen/width]] |Screen width in pixels |
 |[[$:/info/browser/screen/height]] |Screen height in pixels |
+|[[$:/info/browser/darkmode]] |<<.from-version "5.3.7">> Is dark mode preferred? ("yes" or "no") |
+|[[$:/info/darkmode]] |<<.deprecated-since "5.3.7">> Alias for  $:/info/browser/darkmode |
 |[[$:/info/node]] |Running under [[Node.js]]? ("yes" or "no") |
 |[[$:/info/url/full]] |<<.from-version "5.1.14">> Full URL of wiki (eg, ''<<example full>>'') |
 |[[$:/info/url/host]] |<<.from-version "5.1.14">> Host portion of URL of wiki (eg, ''<<example host>>'') |
@@ -28,4 +30,3 @@ System tiddlers in the namespace `$:/info/` are used to expose information about
 |[[$:/info/url/port]] |<<.from-version "5.1.14">> Port portion of URL of wiki (eg, ''<<example port>>'') |
 |[[$:/info/url/protocol]] |<<.from-version "5.1.14">> Protocol portion of URL of wiki (eg, ''<<example protocol>>'') |
 |[[$:/info/url/search]] |<<.from-version "5.1.14">> Search portion of URL of wiki (eg, ''<<example search>>'') |
-|[[$:/info/darkmode]] |<<.from-version "5.1.23">> Is dark mode enabled? ("yes" or "no") |
diff --git a/editions/tw5.com/tiddlers/mechanisms/MediaQueryTrackerMechanism.tid b/editions/tw5.com/tiddlers/mechanisms/MediaQueryTrackerMechanism.tid
new file mode 100644
index 000000000..e050da078
--- /dev/null
+++ b/editions/tw5.com/tiddlers/mechanisms/MediaQueryTrackerMechanism.tid
@@ -0,0 +1,8 @@
+title: MediaQueryTrackerMechanism
+tags: Mechanisms
+
+<<.from-version "5.3.7">> The media query tracker mechanism allows you to define [[custom CSS media queries|https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_media_queries/Using_media_queries]] to be bound to a specified [[info|InfoMechanism]] tiddler. The info tiddler will be dynamically update to reflect the current state of the media query.
+
+Adding or modifying a tiddler tagged $:/tags/MediaQueryTracker takes effect immediately.
+
+The media queries are always applied against the main window. This is relevant for viewport related media queries such as `min-width` which will always respect the main window and ignore the sizes of any external windows.