diff --git a/understanding/toc.html b/understanding/toc.html
index 69620f7579..2b9e001e80 100644
--- a/understanding/toc.html
+++ b/understanding/toc.html
@@ -1,259 +1,153 @@
-<ul class="principal">
+<ul>
 	<li><a href="intro">Introduction to Understanding WCAG 2.1</a></li>
 	<li><a href="understanding-techniques">Understanding Techniques for WCAG Success Criteria</a></li>
-	<li>Perceivable <ul class="guideline">
-		<li>Text Alternatives 
-			<ul class="sc">
-				
-				<li><a href="20/non-text-content.html">Non-text Content</a></li>
-			</ul>
-		</li>
-	</ul>
-		<ul class="guideline">
-			<li>Time-based Media 
-				<ul class="sc">
-					
-					<li><a href="20/audio-only-and-video-only-prerecorded.html">Audio-only and Video-only (Prerecorded)</a></li>
-					
-					<li><a href="20/captions-prerecorded.html">Captions (Prerecorded)</a></li>
-					
-					<li><a href="20/audio-description-or-media-alternative-prerecorded.html">Audio Description or Media Alternative (Prerecorded)</a></li>
-					
-					<li><a href="20/captions-live.html">Captions (Live)</a></li>
-					
-					<li><a href="20/audio-description-prerecorded.html">Audio Description (Prerecorded)</a></li>
-					
-					<li><a href="20/sign-language-prerecorded.html">Sign Language (Prerecorded)</a></li>
-					
-					<li><a href="20/extended-audio-description-prerecorded.html">Extended Audio Description (Prerecorded)</a></li>
-					
-					<li><a href="20/media-alternative-prerecorded.html">Media Alternative (Prerecorded)</a></li>
-					
-					<li><a href="20/audio-only-live.html">Audio-only (Live)</a></li>
+	<li>Perceivable 
+		<ul>
+			<li><a href="text-alternatives">Text Alternatives</a>
+				<ul>
+					<li><a href="non-text-content">Non-text Content</a></li>
 				</ul>
 			</li>
-		</ul>
-		<ul class="guideline">
-			<li>Adaptable 
-				<ul class="sc">
-					
-					<li><a href="20/info-and-relationships.html">Info and Relationships</a></li>
-					
-					<li><a href="20/meaningful-sequence.html">Meaningful Sequence</a></li>
-					
-					<li><a href="20/sensory-characteristics.html">Sensory Characteristics</a></li>
-					
-					<li><a href="21/identify-input-purpose.html">Identify Input Purpose</a></li>
-					
-					<li><a href="21/identify-purpose.html">Identify Purpose</a></li>
+			<li><a href="time-based-media">Time-based Media</a>
+				<ul>
+					<li><a href="audio-only-and-video-only-prerecorded">Audio-only and Video-only (Prerecorded)</a></li>
+					<li><a href="captions-prerecorded">Captions (Prerecorded)</a></li>
+					<li><a href="audio-description-or-media-alternative-prerecorded">Audio Description or Media Alternative (Prerecorded)</a></li>
+					<li><a href="captions-live">Captions (Live)</a></li>
+					<li><a href="audio-description-prerecorded">Audio Description (Prerecorded)</a></li>
+					<li><a href="sign-language-prerecorded">Sign Language (Prerecorded)</a></li>
+					<li><a href="extended-audio-description-prerecorded">Extended Audio Description (Prerecorded)</a></li>
+					<li><a href="media-alternative-prerecorded">Media Alternative (Prerecorded)</a></li>
+					<li><a href="audio-only-live">Audio-only (Live)</a></li>
 				</ul>
 			</li>
-		</ul>
-		<ul class="guideline">
-			<li>Distinguishable 
-				<ul class="sc">
-					
-					<li><a href="20/use-of-color.html">Use of Color</a></li>
-					
-					<li><a href="20/audio-control.html">Audio Control</a></li>
-					
-					<li><a href="20/contrast-minimum.html">Contrast (Minimum)</a></li>
-					
-					<li><a href="20/resize-text.html">Resize text</a></li>
-					
-					<li><a href="20/images-of-text.html">Images of Text</a></li>
-					
-					<li><a href="20/contrast-enhanced.html">Contrast (Enhanced)</a></li>
-					
-					<li><a href="20/low-or-no-background-audio.html">Low or No Background Audio</a></li>
-					
-					<li><a href="20/visual-presentation.html">Visual Presentation</a></li>
-					
-					<li><a href="20/images-of-text-no-exception.html">Images of Text (No Exception)</a></li>
-					
-					<li><a href="21/reflow.html">Reflow</a></li>
-					
-					<li><a href="21/non-text-contrast.html">Non-Text Contrast</a></li>
-					
-					<li><a href="21/text-spacing.html">Text Spacing</a></li>
-					
-					<li><a href="21/content-on-hover-or-focus.html">Content on Hover or Focus</a></li>
+			<li><a href="adaptable">Adaptable</a>
+				<ul>
+					<li><a href="info-and-relationships">Info and Relationships</a></li>
+					<li><a href="meaningful-sequence">Meaningful Sequence</a></li>
+					<li><a href="sensory-characteristics">Sensory Characteristics</a></li>
+					<li><a href="orientation">Orientation</a></li>
+					<li><a href="identify-input-purpose">Identify Input Purpose</a></li>
+					<li><a href="identify-purpose">Identify Purpose</a></li>
+				</ul>
+			</li>
+			<li><a href="distinguishable">Distinguishable</a>
+				<ul>
+					<li><a href="use-of-color">Use of Color</a></li>
+					<li><a href="audio-control">Audio Control</a></li>
+					<li><a href="contrast-minimum">Contrast (Minimum)</a></li>
+					<li><a href="resize-text">Resize text</a></li>
+					<li><a href="images-of-text">Images of Text</a></li>
+					<li><a href="contrast-enhanced">Contrast (Enhanced)</a></li>
+					<li><a href="low-or-no-background-audio">Low or No Background Audio</a></li>
+					<li><a href="visual-presentation">Visual Presentation</a></li>
+					<li><a href="images-of-text-no-exception">Images of Text (No Exception)</a></li>
+					<li><a href="reflow">Reflow</a></li>
+					<li><a href="non-text-contrast">Non-text Contrast</a></li>
+					<li><a href="text-spacing">Text Spacing</a></li>
+					<li><a href="content-on-hover-or-focus">Content on Hover or Focus</a></li>
 				</ul>
 			</li>
 		</ul>
 	</li>
-	<li>Operable <ul class="guideline">
-		<li>Keyboard Accessible 
-			<ul class="sc">
-				
-				<li><a href="20/keyboard.html">Keyboard</a></li>
-				
-				<li><a href="20/no-keyboard-trap.html">No Keyboard Trap</a></li>
-				
-				<li><a href="20/keyboard-no-exception.html">Keyboard (No Exception)</a></li>
-				
-			</ul>
-		</li>
-		
-		
-		<li>Enough Time 
-			<ul class="sc">
-				
-				<li><a href="20/timing-adjustable.html">Timing Adjustable</a></li>
-				
-				<li><a href="20/pause-stop-hide.html">Pause, Stop, Hide</a></li>
-				
-				<li><a href="20/no-timing.html">No Timing</a></li>
-				
-				<li><a href="20/interruptions.html">Interruptions</a></li>
-				
-				<li><a href="20/re-authenticating.html">Re-authenticating</a></li>
-				
-				<li><a href="21/timeouts.html">Timeouts</a></li>
-				
-				<li><a href="21/animation-from-interactions.html">Animation from Interactions</a></li>
-				
-			</ul>
-		</li>
-		
-		
-		<li>Seizures 
-			<ul class="sc">
-				
-				<li><a href="20/three-flashes-or-below-threshold.html">Three Flashes or Below Threshold</a></li>
-				
-				<li><a href="20/three-flashes.html">Three Flashes</a></li>
-				
-			</ul>
-		</li>
-		
-		<li>Navigable 
-			<ul class="sc">
-				
-				<li><a href="20/bypass-blocks.html">Bypass Blocks</a></li>
-				
-				<li><a href="20/page-titled.html">Page Titled</a></li>
-				
-				<li><a href="20/focus-order.html">Focus Order</a></li>
-				
-				<li><a href="20/link-purpose-in-context.html">Link Purpose (In Context)</a></li>
-				
-				<li><a href="20/multiple-ways.html">Multiple Ways</a></li>
-				
-				<li><a href="20/headings-and-labels.html">Headings and Labels</a></li>
-				
-				<li><a href="20/focus-visible.html">Focus Visible</a></li>
-				
-				<li><a href="20/location.html">Location</a></li>
-				
-				<li><a href="20/link-purpose-link-only.html">Link Purpose (Link Only)</a></li>
-				
-				<li><a href="20/section-headings.html">Section Headings</a></li>
-				
-				<li><a href="21/character-key-shortcuts.html">Character-key Shortcuts</a></li>
-				
-				<li><a href="21/label-in-name.html">Label in Name</a></li>
-				
-			</ul>
-		</li>
-		
-		<li><a href="21/pointer-accessible.html">Pointer Accessible</a> 
-			<ul class="sc">
-				<li><a href="21/pointer-gestures.html">Pointer Gestures</a></li>
-				
-				<li><a href="21/pointer-cancellation.html">Pointer Cancellation</a></li>
-				
-				<li><a href="21/target-size-enhanced.html">Target Size (Enhanced)</a></li>
-				
-				<li><a href="21/concurrent-input-mechanisms.html">Concurrent Input Mechanisms</a></li>
-				
-			</ul>
-		</li>
-		
-		
-		<li>Additional sensor inputs 
-			<ul>
-				<li><a href="21/motion-actuation.html">Motion Actuation</a></li>
-				
-				<li><a href="21/orientation.html">Orientation</a></li>
-			</ul>
-		</li>
-		
-	</ul>
+	<li>Operable 
+		<ul>
+			<li><a href="keyboard-accessible">Keyboard Accessible</a>
+				<ul>
+					<li><a href="keyboard">Keyboard</a></li>
+					<li><a href="no-keyboard-trap">No Keyboard Trap</a></li>
+					<li><a href="keyboard-no-exception">Keyboard (No Exception)</a></li>
+					<li><a href="character-key-shortcuts">Character Key Shortcuts</a></li>
+				</ul>
+			</li>
+			<li><a href="enough-time">Enough Time</a>
+				<ul>
+					<li><a href="timing-adjustable">Timing Adjustable</a></li>
+					<li><a href="pause-stop-hide">Pause, Stop, Hide</a></li>
+					<li><a href="no-timing">No Timing</a></li>
+					<li><a href="interruptions">Interruptions</a></li>
+					<li><a href="re-authenticating">Re-authenticating</a></li>
+					<li><a href="timeouts">Timeouts</a></li>
+				</ul>
+			</li>
+			<li><a href="seizures-and-physical-reactions">Seizures and Physical Reactions</a>
+				<ul>
+					<li><a href="three-flashes-or-below-threshold">Three Flashes or Below Threshold</a></li>
+					<li><a href="three-flashes">Three Flashes</a></li>
+					<li><a href="animation-from-interactions">Animation from Interactions</a></li>
+				</ul>
+			</li>
+			<li><a href="navigable">Navigable</a>
+				<ul>
+					<li><a href="bypass-blocks">Bypass Blocks</a></li>
+					<li><a href="page-titled">Page Titled</a></li>
+					<li><a href="focus-order">Focus Order</a></li>
+					<li><a href="link-purpose-in-context">Link Purpose (In Context)</a></li>
+					<li><a href="multiple-ways">Multiple Ways</a></li>
+					<li><a href="headings-and-labels">Headings and Labels</a></li>
+					<li><a href="focus-visible">Focus Visible</a></li>
+					<li><a href="location">Location</a></li>
+					<li><a href="link-purpose-link-only">Link Purpose (Link Only)</a></li>
+					<li><a href="section-headings">Section Headings</a></li>
+				</ul>
+			</li>
+			<li><a href="input-modalities">Input Modalities</a>
+				<ul>
+					<li><a href="pointer-gestures">Pointer Gestures</a></li>
+					<li><a href="pointer-cancellation">Pointer Cancellation</a></li>
+					<li><a href="label-in-name">Label in Name</a></li>
+					<li><a href="motion-actuation">Motion Actuation</a></li>
+					<li><a href="target-size">Target Size</a></li>
+					<li><a href="concurrent-input-mechanisms">Concurrent Input Mechanisms</a></li>
+				</ul>
+			</li>
+		</ul>
 	</li>
-	<li>Understandable <ul class="guideline">
-		
-		<li>Readable 
-			<ul class="sc">
-				
-				<li><a href="20/language-of-page.html">Language of Page</a></li>
-				
-				<li><a href="20/language-of-parts.html">Language of Parts</a></li>
-				
-				<li><a href="20/unusual-words.html">Unusual Words</a></li>
-				
-				<li><a href="20/abbreviations.html">Abbreviations</a></li>
-				
-				<li><a href="20/reading-level.html">Reading Level</a></li>
-				
-				<li><a href="20/pronunciation.html">Pronunciation</a></li>
-				
-			</ul>
-		</li>
-		
-		
-		<li>Predictable 
-			<ul class="sc">
-				
-				<li><a href="20/on-focus.html">On Focus</a></li>
-				
-				<li><a href="20/on-input.html">On Input</a></li>
-				
-				<li><a href="20/consistent-navigation.html">Consistent Navigation</a></li>
-				
-				<li><a href="20/consistent-identification.html">Consistent Identification</a></li>
-				
-				<li><a href="20/change-on-request.html">Change on Request</a></li>
-				
-			</ul>
-		</li>
-		
-		<li>Input Assistance 
-			<ul class="sc">
-				
-				<li><a href="20/error-identification.html">Error Identification</a></li>
-				
-				<li><a href="20/labels-or-instructions.html">Labels or Instructions</a></li>
-				
-				<li><a href="20/error-suggestion.html">Error Suggestion</a></li>
-				
-				<li><a href="20/error-prevention-legal-financial-data.html">Error Prevention (Legal, Financial, Data)</a></li>
-				
-				<li><a href="20/help.html">Help</a></li>
-				
-				<li><a href="20/error-prevention-all.html">Error Prevention (All)</a></li>
-				
-			</ul>
-		</li>
-		
-	</ul>
+	<li>Understandable 
+		<ul>
+			<li><a href="readable">Readable</a>
+				<ul>
+					<li><a href="language-of-page">Language of Page</a></li>
+					<li><a href="language-of-parts">Language of Parts</a></li>
+					<li><a href="unusual-words">Unusual Words</a></li>
+					<li><a href="abbreviations">Abbreviations</a></li>
+					<li><a href="reading-level">Reading Level</a></li>
+					<li><a href="pronunciation">Pronunciation</a></li>
+				</ul>
+			</li>
+			<li><a href="predictable">Predictable</a>
+				<ul>
+					<li><a href="on-focus">On Focus</a></li>
+					<li><a href="on-input">On Input</a></li>
+					<li><a href="consistent-navigation">Consistent Navigation</a></li>
+					<li><a href="consistent-identification">Consistent Identification</a></li>
+					<li><a href="change-on-request">Change on Request</a></li>
+				</ul>
+			</li>
+			<li><a href="input-assistance">Input Assistance</a>
+				<ul>
+					<li><a href="error-identification">Error Identification</a></li>
+					<li><a href="labels-or-instructions">Labels or Instructions</a></li>
+					<li><a href="error-suggestion">Error Suggestion</a></li>
+					<li><a href="error-prevention-legal-financial-data">Error Prevention (Legal, Financial, Data)</a></li>
+					<li><a href="help">Help</a></li>
+					<li><a href="error-prevention-all">Error Prevention (All)</a></li>
+				</ul>
+			</li>
+		</ul>
 	</li>
-	<li>Robust <ul class="guideline">
-		<li>Compatible 
-			<ul class="sc">
-				
-				<li><a href="20/parsing.html">Parsing</a></li>
-				
-				<li><a href="20/name-role-value.html">Name, Role, Value</a></li>
-				
-				<li><a href="21/status-changes.html">Status Changes</a></li>
-				
-			</ul>
-		</li>
-		
-	</ul>
+	<li>Robust 
+		<ul>
+			<li><a href="compatible">Compatible</a>
+				<ul>
+					<li><a href="parsing">Parsing</a></li>
+					<li><a href="name-role-value">Name, Role, Value</a></li>
+					<li><a href="status-messages">Status Messages</a></li>
+				</ul>
+			</li>
+		</ul>
 	</li>
-	<li><a href="conformance">Understanding Conformance</a> </li>
+	<li><a href="conformance">Understanding Conformance</a></li>
 	<li><a href="refer-to-wcag">How to Refer to WCAG 2.1 from Other Documents</a></li>
 	<li><a href="documenting-accessibility-support">Documenting Accessibility Support for Uses of a Web Technology</a></li>
 	<li><a href="understanding-metadata">Understanding Metadata</a></li>