diff --git a/src/wp-admin/js/editor.js b/src/wp-admin/js/editor.js
index 002cf4a11f..17d296276d 100644
--- a/src/wp-admin/js/editor.js
+++ b/src/wp-admin/js/editor.js
@@ -1,43 +1,24 @@
 
 ( function( $ ) {
 	/**
-	 * @summary Creates the tinyMCE editors.
+	 * @summary Utility functions for the editor.
 	 *
-	 * Creates the tinyMCE editor and binds all events used for switching
-	 * from visual to text mode.
-	 *
-	 * @since 4.3.0
-	 *
-	 * @class
+	 * @since 2.5.0
 	 */
 	function SwitchEditors() {
 		var tinymce, $$,
 			exports = {};
 
-		/**
-		 * @summary Initializes the event binding for switching editors.
-		 *
-		 * @since 4.3.0
-		 *
-		 * @returns {void}
-		 */
 		function init() {
 			if ( ! tinymce && window.tinymce ) {
 				tinymce = window.tinymce;
 				$$ = tinymce.$;
 
 				/**
-				 * @summary Handles onclick events for the editor buttons.
+				 * @summary Handles onclick events for the Visual/Text tabs.
 				 *
 				 * @since 4.3.0
 				 *
-				 * Handles an onclick event on the document.
-				 * Switches the editor between visual and text,
-				 * if the clicked element has the 'wp-switch-editor' class.
-				 * If the class name is switch-html switches to the HTML editor,
-				 * if the class name is switch-tmce
-				 * switches to the TMCE editor.
-				 *
 				 * @returns {void}
 				 */
 				$$( document ).on( 'click', function( event ) {
@@ -54,12 +35,11 @@
 		}
 
 		/**
-		 * @summary Retrieves the height of the toolbar based on the container the
-		 * editor is placed in.
+		 * @summary Returns the height of the editor toolbar(s) in px.
 		 *
 		 * @since 3.9.0
 		 *
-		 * @param {Object} editor The tinyMCE editor.
+		 * @param {Object} editor The TinyMCE editor.
 		 * @returns {number} If the height is between 10 and 200 return the height,
 		 * else return 30.
 		 */
@@ -75,17 +55,14 @@
 		}
 
 		/**
-		 * @summary Switches the editor between visual and text.
+		 * @summary Switches the editor between Visual and Text mode.
 		 *
-		 * @since 4.3.0
+		 * @since 2.5.0
 		 *
 		 * @memberof switchEditors
 		 *
-		 * @param {string} id The id of the editor you want to change the editor mode for.
-		 * If no id is given, it defaults to content.
-		 * @param {string} mode The mode you want to switch to.
-		 * If an undefined mode is given, it defaults to toggle.
-		 *
+		 * @param {string} id The id of the editor you want to change the editor mode for. Default: `content`.
+		 * @param {string} mode The mode you want to switch to. Default: `toggle`.
 		 * @returns {void}
 		 */
 		function switchEditor( id, mode ) {
@@ -98,7 +75,6 @@
 				$textarea = $$( '#' + id ),
 				textarea = $textarea[0];
 
-			// Toggle the mode between visual and textual representation.
 			if ( 'toggle' === mode ) {
 				if ( editor && ! editor.isHidden() ) {
 					mode = 'html';
@@ -107,20 +83,13 @@
 				}
 			}
 
-
-			// If the mode is tmce or tinymce, show the editor.
 			if ( 'tmce' === mode || 'tinymce' === mode ) {
-
-				/*
-				 * If the editor isn't hidden we are already in tmce mode
-				 * and we don't need to switch.
-				 * Return false to stop event bubbling.
-				 */
+				// If the editor is visible we are already in `tinymce` mode.
 				if ( editor && ! editor.isHidden() ) {
 					return false;
 				}
 
-				// Close the QuickTags toolbars if they are visible.
+				// Insert closing tags for any open tags in QuickTags.
 				if ( typeof( window.QTags ) !== 'undefined' ) {
 					window.QTags.closeAllTags( id );
 				}
@@ -130,12 +99,12 @@
 				if ( editor ) {
 					editor.show();
 
-					// Don't resize the iframe in iOS.
+					// No point to resize the iframe in iOS.
 					if ( ! tinymce.Env.iOS && editorHeight ) {
 						toolbarHeight = getToolbarHeight( editor );
 						editorHeight = editorHeight - toolbarHeight + 14;
 
-						// Height must be between 50 and 5000.
+						// Sane limit for the editor height.
 						if ( editorHeight > 50 && editorHeight < 5000 ) {
 							editor.theme.resizeTo( null, editorHeight );
 						}
@@ -148,21 +117,14 @@
 				$textarea.attr( 'aria-hidden', true );
 				window.setUserSetting( 'editor', 'tinymce' );
 
-			// Hide the editor if mode is html.
 			} else if ( 'html' === mode ) {
-
-				/*
-				 * If the editor is hidden we are already in html mode and
-				 * we don't need to switch.
-				 * Return false to stop event bubbling.
-				 */
+				// If the editor is hidden (Quicktags is shown) we don't need to switch.
 				if ( editor && editor.isHidden() ) {
 					return false;
 				}
 
 				if ( editor ) {
-
-					// Don't resize the iframe in iOS.
+					// Don't resize the textarea in iOS. The iframe is forced to 100% height there, we shouldn't match it.
 					if ( ! tinymce.Env.iOS ) {
 						iframe = editor.iframeElement;
 						editorHeight = iframe ? parseInt( iframe.style.height, 10 ) : 0;
@@ -171,7 +133,7 @@
 							toolbarHeight = getToolbarHeight( editor );
 							editorHeight = editorHeight + toolbarHeight - 14;
 
-							// Height must be between 50 and 5000.
+							// Sane limit for the textarea height.
 							if ( editorHeight > 50 && editorHeight < 5000 ) {
 								textarea.style.height = editorHeight + 'px';
 							}
@@ -180,7 +142,7 @@
 
 					editor.hide();
 				} else {
-					// The TinyMCE instance doesn't exist, show the textarea.
+					// There is probably a JS error on the page. The TinyMCE editor instance doesn't exist. Show the textarea.
 					$textarea.css({ 'display': '', 'visibility': '' });
 				}
 
@@ -191,20 +153,18 @@
 		}
 
 		/**
-		 * @summary Replaces all paragraphs with double line breaks.
+		 * @summary Replaces <p> tags with two line breaks. "Opposite" of wpautop().
 		 *
-		 * Replaces all paragraphs with double line breaks. Taking into account
-		 * the elements where the <p> should be preserved.
-		 * Unifies all whitespaces.
-		 * Adds indenting with tabs to li, dt and dd elements.
-		 * Trims whitespaces from beginning and end of the html input.
+		 * Replaces <p> tags with two line breaks except where the <p> has attributes.
+		 * Unifies whitespace.
+		 * Indents <li>, <dt> and <dd> for better readability.
 		 *
-		 * @since 4.3.0
+		 * @since 2.5.0
 		 *
 		 * @memberof switchEditors
 		 *
 		 * @param {string} html The content from the editor.
-		 * @return {string} The formatted html string.
+		 * @return {string} The content with stripped paragraph tags.
 		 */
 		function removep( html ) {
 			var blocklist = 'blockquote|ul|ol|li|dl|dt|dd|table|thead|tbody|tfoot|tr|th|td|h[1-6]|fieldset',
@@ -218,10 +178,7 @@
 				return '';
 			}
 
-			/*
-			 * Protect script and style tags by replacing them with <wp-preserve>.
-			 * Push matches into the preserve array.
-			 */
+			// Protect script and style tags.
 			if ( html.indexOf( '<script' ) !== -1 || html.indexOf( '<style' ) !== -1 ) {
 				html = html.replace( /<(script|style)[^>]*>[\s\S]*?<\/\1>/g, function( match ) {
 					preserve.push( match );
@@ -229,10 +186,7 @@
 				} );
 			}
 
-			/*
-			 * Protect pre tags by replacing all newlines and
-			 * <br> tags with <wp-line-break>.
-			 */
+			// Protect pre tags.
 			if ( html.indexOf( '<pre' ) !== -1 ) {
 				preserve_linebreaks = true;
 				html = html.replace( /<pre[^>]*>[\s\S]+?<\/pre>/g, function( a ) {
@@ -242,10 +196,7 @@
 				});
 			}
 
-			/*
-			 * Keep <br> tags inside captions and remove line breaks by replacing
-			 * them with <wp-temp-br>.
-			 */
+			// Remove line breaks but keep <br> tags inside image captions.
 			if ( html.indexOf( '[caption' ) !== -1 ) {
 				preserve_br = true;
 				html = html.replace( /\[caption[\s\S]+?\[\/caption\]/g, function( a ) {
@@ -253,65 +204,53 @@
 				});
 			}
 
-			// Format the text to be readable in the source editor.
+			// Normalize white space characters before and after block tags.
 			html = html.replace( new RegExp( '\\s*</(' + blocklist1 + ')>\\s*', 'g' ), '</$1>\n' );
 			html = html.replace( new RegExp( '\\s*<((?:' + blocklist1 + ')(?: [^>]*)?)>', 'g' ), '\n<$1>' );
 
 			// Mark </p> if it has any attributes.
 			html = html.replace( /(<p [^>]+>.*?)<\/p>/g, '$1</p#>' );
 
-			// If the content of a container starts with a paragraph, replace the <p> tag with 2 newlines.
+			// Preserve the first <p> inside a <div>.
 			html = html.replace( /<div( [^>]*)?>\s*<p>/gi, '<div$1>\n\n' );
 
-			// Remove <p> and </p> tags.
+			// Remove paragraph tags.
 			html = html.replace( /\s*<p>/gi, '' );
 			html = html.replace( /\s*<\/p>\s*/gi, '\n\n' );
 
-			// Remove white spaces between newlines. u00a0 is a no breaking space.
+			// Normalize white space chars and remove multiple line breaks.
 			html = html.replace( /\n[\s\u00a0]+\n/g, '\n\n' );
 
-			// Remove <br> tags.
+			// Rrplace <br> tags with a line break.
 			html = html.replace( /\s*<br ?\/?>\s*/gi, '\n' );
 
-			/*
-			 * Fix some block element newline issues.
-			 * Replace white spaces with newlines in combination with <div> tags.
-			 */
+			// Fix line breaks around <div>.
 			html = html.replace( /\s*<div/g, '\n<div' );
 			html = html.replace( /<\/div>\s*/g, '</div>\n' );
 
-			// Replace white spaces with newlines in combination with [caption] shortcodes.
+			// Fix line breaks around caption shortcodes.
 			html = html.replace( /\s*\[caption([^\[]+)\[\/caption\]\s*/gi, '\n\n[caption$1[/caption]\n\n' );
-
-			/*
-			 * Limit the newlines in combination with [caption]'s to a maximum of
-			 * two consecutive occurrences.
-			 * .
-			 */
 			html = html.replace( /caption\]\n\n+\[caption/g, 'caption]\n\n[caption' );
 
-			/*
-			 * Replace white spaces with newlines in combination with
-			 * all elements listed in blocklist2.
-			 */
+			// Pad block elements tags with a line break.
 			html = html.replace( new RegExp('\\s*<((?:' + blocklist2 + ')(?: [^>]*)?)\\s*>', 'g' ), '\n<$1>' );
 			html = html.replace( new RegExp('\\s*</(' + blocklist2 + ')>\\s*', 'g' ), '</$1>\n' );
 
-			// Add indentation by adding a tab in front of <li>, <dt> and <dd> tags.
+			// Indent <li>, <dt> and <dd> tags.
 			html = html.replace( /<((li|dt|dd)[^>]*)>/g, ' \t<$1>' );
 
-			// Replace white spaces with newlines in combination with <select> and <option> tags.
+			// Fix line breaks around <select> and <option>.
 			if ( html.indexOf( '<option' ) !== -1 ) {
 				html = html.replace( /\s*<option/g, '\n<option' );
 				html = html.replace( /\s*<\/select>/g, '\n</select>' );
 			}
 
-			// Replace white spaces with 2 newlines in combination with <hr> tags.
+			// Pad <hr> with two line breaks.
 			if ( html.indexOf( '<hr' ) !== -1 ) {
 				html = html.replace( /\s*<hr( [^>]*)?>\s*/g, '\n\n<hr$1>\n\n' );
 			}
 
-			// Remove newlines in <object> tags.
+			// Remove line breaks in <object> tags.
 			if ( html.indexOf( '<object' ) !== -1 ) {
 				html = html.replace( /<object[\s\S]+?<\/object>/g, function( a ) {
 					return a.replace( /[\r\n]+/g, '' );
@@ -321,23 +260,17 @@
 			// Unmark special paragraph closing tags.
 			html = html.replace( /<\/p#>/g, '</p>\n' );
 
-
-			// Add a new line before <p> tags when there is content inside the paragraph
+			// Pad remaining <p> tags whit a line break.
 			html = html.replace( /\s*(<p [^>]+>[\s\S]*?<\/p>)/g, '\n$1' );
 
-			/*
-			 * Remove whitespaces at the start and end of a string.
-			 * u00a0 is a no breaking space.
-			 */
+			// Trim.
 			html = html.replace( /^\s+/, '' );
 			html = html.replace( /[\s\u00a0]+$/, '' );
 
-			// Replace <wp-line-break> tags with a newline.
 			if ( preserve_linebreaks ) {
 				html = html.replace( /<wp-line-break>/g, '\n' );
 			}
 
-			// Restore the <wp-temp-br> with <br> tags.
 			if ( preserve_br ) {
 				html = html.replace( /<wp-temp-br([^>]*)>/g, '<br$1>' );
 			}
@@ -353,14 +286,11 @@
 		}
 
 		/**
-		 * @summary Adds paragraph tags to the text.
-		 *
-		 * Adds paragraph tags to the text taking into account block level elements.
-		 * Normalizes the whitespaces and newlines.
+		 * @summary Replaces two line breaks with a paragraph tag and one line break with a <br>.
 		 *
 		 * Similar to `wpautop()` in formatting.php.
 		 *
-		 * @since 4.3.0
+		 * @since 2.5.0
 		 *
 		 * @memberof switchEditors
 		 *
@@ -370,8 +300,6 @@
 		function autop( text ) {
 			var preserve_linebreaks = false,
 				preserve_br = false,
-
-				// A list containing all block level elements.
 				blocklist = 'table|thead|tfoot|caption|col|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre' +
 					'|form|map|area|blockquote|address|math|style|p|h[1-6]|hr|fieldset|legend|section' +
 					'|article|aside|hgroup|header|footer|nav|figure|figcaption|details|menu|summary';
@@ -379,25 +307,23 @@
 			// Normalize line breaks.
 			text = text.replace( /\r\n|\r/g, '\n' );
 
-			// If there are no newlines, return the text.
 			if ( text.indexOf( '\n' ) === -1 ) {
 				return text;
 			}
 
+			// Remove line breaks from <object>.
 			if ( text.indexOf( '<object' ) !== -1 ) {
-
-				// If there are multiple newlines in an <object>, remove them.
 				text = text.replace( /<object[\s\S]+?<\/object>/g, function( a ) {
 					return a.replace( /\n+/g, '' );
 				});
 			}
 
-			// Replace all new lines and tabs with spaces inside tags.
+			// Remove line breaks from tags.
 			text = text.replace( /<[^<>]+>/g, function( a ) {
 				return a.replace( /[\n\t ]+/g, ' ' );
 			});
 
-			// Protect <pre> and <script> tags by replacing them with <wp-line-break>.
+			// Preserve line breaks in <pre> and <script> tags.
 			if ( text.indexOf( '<pre' ) !== -1 || text.indexOf( '<script' ) !== -1 ) {
 				preserve_linebreaks = true;
 				text = text.replace( /<(pre|script)[^>]*>[\s\S]*?<\/\1>/g, function( a ) {
@@ -409,125 +335,68 @@
 			if ( text.indexOf( '[caption' ) !== -1 ) {
 				preserve_br = true;
 
-				// Replace all white spaces and <br> tags with <wp-temp-br>.
 				text = text.replace( /\[caption[\s\S]+?\[\/caption\]/g, function( a ) {
-
-					// Protect <br> tags by converting them to <wp-temp-br> tags.
 					a = a.replace( /<br([^>]*)>/g, '<wp-temp-br$1>' );
 
-					// Replace all new lines and tabs with spaces inside HTML tags.
 					a = a.replace( /<[^<>]+>/g, function( b ) {
-
-						// Replace newlines and tabs with a space.
 						return b.replace( /[\n\t ]+/, ' ' );
 					});
 
-					// Convert remaining line breaks to <wp-temp-br />.
 					return a.replace( /\s*\n\s*/g, '<wp-temp-br />' );
 				});
 			}
 
-			// Append 2 newlines at the end of the text.
 			text = text + '\n\n';
-
-			/*
-			 * Replace a <br> tag followed by 1 or more spaces
-			 * and another <br> tag with 2 newlines.
-			 */
 			text = text.replace( /<br \/>\s*<br \/>/gi, '\n\n' );
 
-			/*
-			 * Replace a block level element open tag with 2 newlines
-			 * followed by the captured block level element.
-			 */
+			// Pad block tags with two line breaks.
 			text = text.replace( new RegExp( '(<(?:' + blocklist + ')(?: [^>]*)?>)', 'gi' ), '\n\n$1' );
-
-			/*
-			 * Replace a block level element closing tag with the captured
-			 * block level element followed by 2 newlines.
-			 */
 			text = text.replace( new RegExp( '(</(?:' + blocklist + ')>)', 'gi' ), '$1\n\n' );
-
-			// Add 2 newlines to a <hr> tag. <hr> is a self closing block element.
 			text = text.replace( /<hr( [^>]*)?>/gi, '<hr$1>\n\n' );
 
-			// Remove the spaces before an <option> tag.
+			// Remove white space chars around <option>.
 			text = text.replace( /\s*<option/gi, '<option' );
-
-			// Remove the spaces after an <option> closing tag.
 			text = text.replace( /<\/option>\s*/gi, '</option>' );
 
-			// Remove the spaces between two newlines.
+			// Normalize multiple line breaks and white space chars.
 			text = text.replace( /\n\s*\n+/g, '\n\n' );
 
-			// Convert 2 newlines to a paragraph and a single newline.
+			// Convert two line breaks to a paragraph.
 			text = text.replace( /([\s\S]+?)\n\n/g, '<p>$1</p>\n' );
 
 			// Remove empty paragraphs.
 			text = text.replace( /<p>\s*?<\/p>/gi, '');
 
-			// Remove spaces and <p> tags around block level elements.
+			// Remove <p> tags that are around block tags.
 			text = text.replace( new RegExp( '<p>\\s*(</?(?:' + blocklist + ')(?: [^>]*)?>)\\s*</p>', 'gi' ), '$1' );
-
-			// Remove <p> tags around li elements.
 			text = text.replace( /<p>(<li.+?)<\/p>/gi, '$1');
 
-			// Remove spaces and <p> tags from blockquotes.
+			// Fix <p> in blockquotes.
 			text = text.replace( /<p>\s*<blockquote([^>]*)>/gi, '<blockquote$1><p>');
-
-			// Place the <blockquote> outside of the paragraph.
 			text = text.replace( /<\/blockquote>\s*<\/p>/gi, '</p></blockquote>');
 
-			// Remove spaces at the start and <p> tags from block level elements.
+			// Remove <p> tags that are wrapped around block tags.
 			text = text.replace( new RegExp( '<p>\\s*(</?(?:' + blocklist + ')(?: [^>]*)?>)', 'gi' ), '$1' );
-
-			// Remove spaces at the end and <p> tags from block level elements.
 			text = text.replace( new RegExp( '(</?(?:' + blocklist + ')(?: [^>]*)?>)\\s*</p>', 'gi' ), '$1' );
 
-			// Remove spaces and newlines after a <br> tag.
 			text = text.replace( /(<br[^>]*>)\s*\n/gi, '$1' );
 
-			// Replace spaces followed by a newline with a <br> tag followed by a new line.
+			// Add <br> tags.
 			text = text.replace( /\s*\n/g, '<br />\n');
 
-			// Remove <br> tag that follows a block element directly, ignoring spaces.
+			// Remove <br> tags that are around block tags.
 			text = text.replace( new RegExp( '(</?(?:' + blocklist + ')[^>]*>)\\s*<br />', 'gi' ), '$1' );
-
-			/*
-			 * Remove a br tag preceding white spaces followed by a
-			 * <p>, <li>, <div>, <dl>, <dd>, <dt>, <th>, <pre>, <td>, <ul>, or <ol> tag.
-			 */
 			text = text.replace( /<br \/>(\s*<\/?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)>)/gi, '$1' );
 
-			// Remove white spaces, <p> and <br> tags in captions.
+			// Remove <p> and <br> around captions.
 			text = text.replace( /(?:<p>|<br ?\/?>)*\s*\[caption([^\[]+)\[\/caption\]\s*(?:<\/p>|<br ?\/?>)*/gi, '[caption$1[/caption]' );
 
-			/**
-			 * @summary Makes sure there is a paragraph open tag for a close tag.
-			 *
-			 * @since 2.9.0
-			 *
-			 * Makes sure there is a paragraph open tag when there is a paragraph close tag
-			 * in a div, th, td, form, fieldset or dd element.
-			 * @param {string} a The complete match.
-			 * @param {string} b The first capture group.
-			 * @param {string} c The second capture group.
-			 * @returns {string} The string in paragraph tags.
-			 */
+			// Make sure there is <p> when there is </p> inside block tags that can contain other blocks.
 			text = text.replace( /(<(?:div|th|td|form|fieldset|dd)[^>]*>)(.*?)<\/p>/g, function( a, b, c ) {
-
-				/*
-				 * Check if the matched group has a p open tag in it. If so, we don't need to
-				 * enclose it with a paragraph.
-				 */
 				if ( c.match( /<p( [^>]*)?>/ ) ) {
 					return a;
 				}
 
-				/*
-				 * If there is no p open tag in the matched string,
-				 * add it and return the string including p tags.
-				 */
 				return b + '<p>' + c + '</p>';
 			});
 
@@ -545,19 +414,14 @@
 		}
 
 		/**
-		 * @summary Modifies the data when a switch is made from HTML to text.
+		 * @summary Fires custom jQuery events `beforePreWpautop` and `afterPreWpautop` when jQuery is available.
 		 *
-		 * Modifies the data when a switch is made.
-		 * Remove the <p> tags from text.
-		 * Returns the modified text.
-		 * Adds a trigger on beforePreWpautop and afterPreWpautop.
-		 *
-		 * @since 2.5.0
+		 * @since 2.9.0
 		 *
 		 * @memberof switchEditors
 		 *
 		 * @param {String} html The content from the visual editor.
-		 * @returns {String} the modified text.
+		 * @returns {String} the filtered content.
 		 */
 		function pre_wpautop( html ) {
 			var obj = { o: exports, data: html, unfiltered: html };
@@ -576,17 +440,14 @@
 		}
 
 		/**
-		 * @summary Modifies the data when a switch is made from text to HTML.
+		 * @summary Fires custom jQuery events `beforeWpautop` and `afterWpautop` when jQuery is available.
 		 *
-		 * Modifies the data when a switch is made. Runs autop to add p tags from text.
-		 * Returns the modified text. Adds a trigger on beforeWpautop and afterWpautop.
-		 *
-		 * @since 2.5.0
+		 * @since 2.9.0
 		 *
 		 * @memberof switchEditors
 		 *
 		 * @param {String} text The content from the text editor.
-		 * @returns {String} the modified text.
+		 * @returns {String} filtered content.
 		 */
 		function wpautop( text ) {
 			var obj = { o: exports, data: text, unfiltered: text };
@@ -604,18 +465,12 @@
 			return obj.data;
 		}
 
-		// Bind the init function to be run when the document is loaded.
 		if ( $ ) {
 			$( document ).ready( init );
 		} else if ( document.addEventListener ) {
-
-			// Use the addEventListener to bind the init event on document load.
 			document.addEventListener( 'DOMContentLoaded', init, false );
 			window.addEventListener( 'load', init, false );
-
 		} else if ( window.attachEvent ) {
-
-			// Use the addEvent to bind the init event on document load.
 			window.attachEvent( 'onload', init );
 			document.attachEvent( 'onreadystatechange', function() {
 				if ( 'complete' === document.readyState ) {
@@ -624,10 +479,6 @@
 			} );
 		}
 
-		/*
-		 * Make sure the window.wp object exists so autop and removep
-		 * can be bound to it.
-		 */
 		window.wp = window.wp || {};
 		window.wp.editor = window.wp.editor || {};
 		window.wp.editor.autop = wpautop;