Added help screen

options.css

+/***********/
+/* GENERAL */
+/***********/
+
 html {
 	box-sizing: border-box;
 	font-size: 16px;
 *, *::before, *::after {
 	box-sizing: inherit;
 }
+
 body {
 	margin: 0 auto;
 	display: flex;
 	padding: 10px 20px;
 	font-size: 1rem;
 }
+body.noscroll {
+	overflow: hidden;
+}
+
 body > div {
 	position: relative;
 }
 body > div + div {
 	margin: 2.5em 0 1em 0;
 }
+
+/************/
+/* HEADINGS */
+/************/
+
 h1 {
 	border-bottom: 1px solid #ddd;
 	margin: 0.5em 0;
 }
 h2 {
 	margin: 0;
-	background-color: #fff;
 	border-bottom: 1px solid #ddd;
 	font-size: 1.625rem;
 	padding: 0 0 2px 0;
 }
+h3 {
+	font-size: 1.3125rem;
+	color: #666;
+	border-bottom: 1px dotted #eee;
+	margin: 1em 0 0.5em 0;
+}
+
+/*************/
+/* TEXTAREAS */
+/*************/
+
 textarea {
 	border: 1px solid #aaa;
 	font-family: Inconsolata, Courier, monospace;
 #exclusionPatterns textarea {
 	min-height: 150px;
 }
-form {
+
+/******************/
+/* OTHER CONTROLS */
+/******************/
+
+.top-controls {
 	text-align: right;
 	margin: 0 0 2.5em 0;
 	display: flex;
+	flex-flow: row wrap;
 	align-items: center;
 	max-width: 640px;
 }
-form .buttons {
+.top-controls .buttons {
 	display: flex;
 	align-items: center;
 	justify-content: flex-end;
 button {
 	-webkit-appearance: none;
 	-moz-appearance: none;
+	border: none;
+	background-color: transparent;
+}
+button:active {
+	transform: scale(0.95);
+}
+button:focus:active {
+	outline: none;
+}
+.top-controls button {
 	border: 1px solid #bbb;
 	color: #fff;
 	padding: 10px 16px;
 	cursor: default;
 	margin: 0 0 0 0.5em;
+	background-color: #fff;
 }
-button.save-button {
+.top-controls button.save-button {
 	background-color: #16e;
 	font-size: 1.5rem;
 }
-button.reset-button {
+.top-controls button.reset-button {
 	background-color: #d3453d;
 	font-size: 1rem;
 }
-button:active {
-	transform: scale(0.95);
-}
-button:focus:active {
-	outline: none;
-}
-button:disabled {
+.top-controls button:disabled {
 	background-color: #777;
 	opacity: 0.3;
 }
 .mode-select-container span:not(.disabled):hover {
 	border-bottom: 1px solid currentColor;
 }
-form button:not(:disabled):hover {
+.top-controls button:not(:disabled):hover {
 	text-shadow:
 		0 0 1px #fff,
 		0 0 3px #fff,
 		0 0 5px #fff;
 	cursor: pointer;
 }
+p.note {
+	font-size: 0.875em;
+}
+
+/******************/
+/* WHITELIST MODE */
+/******************/
+
 #matchingPatterns.disabled h2 {
 	color: rgba(0,0,0,0.15);
 }
 	font-family: Inconsolata, Courier, monospace;
 	font-size: 4em;
 }
-p.note {
-	font-size: 0.875em;
-}
+
+/***************/
+/* BOTTOM INFO */
+/***************/
+
 .bottom-info {
 	font-size: 0.875rem;
 	color: #aaa;
 }
 .bottom-info p {
 	margin: 0;
-}
+}
+
+/****************/
+/* HELP OVERLAY */
+/****************/
+
+.open-help-button-container {
+	position: absolute;
+	top: 0;
+	right: 0;
+}
+
+.help-overlay {
+	position: fixed;
+	background-color: #ffe;
+	top: 10px;
+	left: 10px;
+	margin: 0;
+	border: 1px solid #777;
+	box-shadow:
+		1px 1px 4px 0 #aaa;
+	width: calc(100% - 20px);
+	height: calc(100% - 20px);
+	line-height: 1.4;
+	padding: 36px 0 6px 0;
+}
+#help {
+	visibility: hidden;
+}
+#help:target {
+	visibility: visible;
+}
+.help-container {
+	height: 100%;
+	padding: 0 16px;
+	overflow-y: scroll;
+}
+.help-container::-webkit-scrollbar {
+	background-color: transparent;
+	width: 15px;
+}
+.help-container::-webkit-scrollbar-thumb {
+	background-color: #c1c1c1;
+	box-shadow: 0 0 0 3px #ffe inset;
+}
+.help-container::-webkit-scrollbar-thumb:hover {
+	background-color: #888;
+}
+
+.help-overlay h1 {
+	margin: 0 0 0.5em 0;
+	line-height: 1;
+	padding: 0 0 4px 0;
+}
+
+.help-overlay .close-button,
+.open-help-button-container .open-help-button {
+	display: block;
+	cursor: pointer;
+	color: #999;
+	white-space: nowrap;
+}
+.help-overlay .close-button:hover,
+.open-help-button-container .open-help-button:hover {
+	color: #000;
+}
+.help-overlay .close-button::before,
+.open-help-button-container .open-help-button::before {
+	font-family: Font Awesome;
+	padding: 4px;
+	display: inline-block;
+}
+
+.help-overlay .close-button {
+	font-size: 0.875rem;
+	position: absolute;
+	top: 0;
+	right: 0;
+	padding: 6px 12px;
+}
+.help-overlay .close-button::before {
+	content: "\F00D";
+	font-weight: 300;
+	font-size: 1rem;
+	position: relative;
+	top: 1px;
+}
+
+.open-help-button-container .open-help-button {
+	font-size: 1.125rem;
+	padding: 8px 12px 10px 10px;
+}
+.open-help-button-container .open-help-button::before {
+	content: "\F059";
+	font-weight: 900;
+	font-size: 1rem;
+}
+
+/********/
+/* MISC */
+/********/
+
+code {
+	font-family: Inconsolata, monospace;
+}
+.fa {
+	font-family: Font Awesome;
+}
+.fa-light {
+	font-weight: 300;
+}
+.fa-normal {
+	font-weight: 400;
+}
+.fa-heavy {
+	font-weight: 900;
+}

options.html

 <!DOCTYPE html>
 <html>
 <head>
-	<title>Always Kill Sticky - Options</title>
+	<title>AlwaysKillSticky - Options</title>
 	<meta name="viewport" content="width=device-width, initial-scale=1" />
 	<meta http-equiv='Content-Type' content='text/html; charset=utf-8' />
 	<link rel='stylesheet' type='text/css' href='options.css' />
+	<link rel='stylesheet' type='text/css' href='fonts.css' />
 	<link rel="shortcut icon" type="image/png" href="images/ASK_on_32.png" />
 </head>
 <body>
-	<h1>Always Kill Sticky</h1>
-	<form>
+	<h1>AlwaysKillSticky</h1>
+	<form class='top-controls'>
 		<span class='mode-select-container'>
 			<span class='blacklist-mode-label'>Blacklist mode</span>
 			<input type='checkbox' id='whitelist-mode'></input>
 		<p class='bottom-info'>AlwaysKillSticky v<span class='version'>0.0</span></p>
 		<p class='bottom-info'>© Said Achmiz 2019–present</p>
 	</div>
+	<form class='open-help-button-container'>
+		<button type='button' class='open-help-button'>Help</button>
+	</form>
+	<div id='help' class='help-overlay'>
+		<form>
+			<button type='button' class='close-button'>Close</button>
+		</form>
+		<div class='help-container'>
+			<h1>AlwaysKillSticky Help</h1>
+			<p>On sites/pages where it’s enabled, AlwaysKillSticky finds all elements whose <code>position</code> CSS property has a computed value of either <code>sticky</code> or <code>fixed</code>, and removes those elements.</p>
+			<h2>Basic usage</h2>
+			<p>To enable AlwaysKillSticky on a site, click the AlwaysKillSticky icon in your browser toolbar, then click the big button (shaped like a thumbtack: <span class='fa fa-heavy'>&#xf08d;</span>). Stickies will immediately be killed, and will always be killed whenever you visit that page, or any page on the same site, in the future.</p>
+			<p>To stop killing stickies on a site, just click the big button again. Stickies will no longer be killed when you visit pages on that site. (After disabling sticky-killing for a page, you can click the Reload (<span class='fa fa-heavy'>&#xf2f1;</span>) button to refresh the page if you want to restore killed sticky elements on that page.)</p>
+			<h2>Modes</h2>
+			<p>AlwaysKillSticky can work in either of two modes: <strong>blacklist mode</strong> (the default) and <strong>whitelist mode</strong>. (You can switch modes at any time, via the Options page.)</p>
+			<h3>Blacklist mode</h3>
+			<p>In <strong>blacklist mode</strong>, stickies will <em>only</em> be killed if:</p>
+			<ul>
+			<li>the page URL matches one of the patterns in the <strong>matching patterns</strong> list, <em>and</em>;</li>
+			<li>the page does <em>not</em> match any of the patterns in the <strong>exclusion patterns</strong> list.</li>
+			</ul>
+			<p>In blacklist mode, if you click the big button (<span class='fa fa-heavy'>&#xf08d;</span>) in the AlwaysKillSticky popup to enable the 
+			<h3>Whitelist mode</h3>
+			<p>In <strong>whitelist mode</strong>, <em>the matching patterns list is ignored</em>. Stickies are <em>always</em> killed, <em>unless</em> the page matches one of the patterns in the <strong>exclusion patterns</strong> list.</p>
+			<p>(In whitelist mode, the behavior of the main button (<span class='fa fa-heavy'>&#xf08d;</span>) in the AlwaysKillSticky popup is reversed.)</p>
+			<h2>Advanced usage</h2>
+			<p>AlwaysKillSticky automatically manages the lists of matching and exclusion patterns. When you enable or disable sticky-killing for a site (by clicking the big button in the AlwaysKillSticky popup), the pattern lists are automatically modified appropriately. There is usually no need to edit the lists yourself.</p>
+			<p>However, if you prefer more fine-grained control (e.g., if you want to kill stickies on all sites on a domain, or if you want to exclude specific paths of a site), you can edit the pattern lists by hand. The matching and exclusion patterns are <a href='https://en.wikipedia.org/wiki/Regular_expression' rel='nofollow' target='_blank'>regular expressions</a> (a.k.a. “regexps”). (The site <a href='https://regexr.com/' rel='nofollow' target='_blank'>RegExr.com</a> is useful if you are not entirely familiar with how regexps work—or even if you are.)</p>
+			<p><strong>NOTE:</strong> Lines beginning with a pound sign (#) are comments; they are ignored.</p>
+			<h3>How automatic management of the patterns lists works</h3>
+			<p>The comments in the <a href='popup.js' target='_blank'><code>popup.js</code> script file</a> explain exactly what happens to the patterns lists when you use the main button (<span class='fa fa-heavy'>&#xf08d;</span>) in the AlwaysKillSticky popup to enable or disable sticky-killing on a site.</p>
+			<h2>License</h2>
+			<p>This extension is released under the GNU General Public License
+			as published by the Free Software Foundation; either version
+			2 of the License, or (at your option) any later version.</p>
+		</div>
+	</div>
 </body>
 <script src="functions.js"></script>
 <script src="options.js"></script>

options.js

 /**********/
 
 /*	Triggered when a click is received by the mode selector switch, or by 
-	either of the two labels (“Blacklist” and “Whitelist”).
+	either of the two labels ("Blacklist" and "Whitelist").
 	*/
 function modeSelectorInputReceived() {
 	toggleModeSelectorState();
 
-	// Activate the “Reset” and “Save” buttons, since changes have been made.
+	// Activate the "Reset" and "Save" buttons, since changes have been made.
 	setButtonsActive(true);
 }
 
 	container.classList.toggle("whitelist", (newMode == "whitelist"));
 	checkbox.checked = (newMode == "whitelist");
 
-	/*	Enable both spans (the “Blacklist” and “Whitelist” labels, then disable 
+	/*	Enable both spans (the "Blacklist" and "Whitelist" labels, then disable 
 		just the label associated with the now-enabled mode. */
 	container.querySelectorAll("span").forEach(span => {
 		span.classList.toggle("disabled", false);
 
 	/*	In whitelist mode, the matching patterns textarea must be disabled,
 		since the matching patterns list is treated as containing only the 
-		single pattern “.*”. An overlay is shown, to indicate this. */
+		single pattern ".*". An overlay is shown, to indicate this. */
 	document.querySelector("div#matchingPatterns").classList.toggle("disabled", (newMode == "whitelist"));
 	document.querySelector("div#matchingPatterns textarea").disabled = (newMode == "whitelist");
 }
 
 /*	Saves the entered state in storage.
-	De-activate the “Reset” and “Save” buttons.
+	De-activate the "Reset" and "Save" buttons.
 	*/
 function saveChanges() {
 	let matchingPatterns = document.querySelector("#matchingPatterns textarea").value;
 }
 
 /*	Retrieves the saved state from storage and reset the UI to reflect it, 
-	discarding the user’s changes.
+	discarding the user's changes.
 	*/
 function resetChanges(callback) {
 	chrome.storage.sync.get([ "matchingPatterns", "exclusionPatterns", "mode" ], (result) => {
 
 		toggleModeSelectorState(AKS.mode);
 
-		// De-activate the “Reset” and “Save” buttons.
+		// De-activate the "Reset" and "Save" buttons.
 		setButtonsActive(false);
 
 		// Expand all textareas.
 	});
 }
 
-/*	Activates or de-activates the “Reset” and “Save” buttons. Called when 
+/*	Activates or de-activates the "Reset" and "Save" buttons. Called when 
 	changes are made (to activate) or when changes are saved or reset (to 
 	de-activate).
 	*/
 function setButtonsActive(active) {
-	document.querySelectorAll("button").forEach(button => {
+	document.querySelectorAll(".top-controls button").forEach(button => {
 		button.disabled = !active;
 	});
 }
 
+/*	Enables or disables scrolling on the page body, depending on whether the
+	help overlay is visible. */
+function setBodyScrollState() {
+	document.querySelector("body").classList.toggle("noscroll", location.hash == "#help");
+}
+
 /*	Expands a textarea to show all its contents (up to a maximum height which is
 	set via CSS).
 	*/
 	});
 }
 
+function setHelpOverlayVisible(visible) {
+	location.hash = visible ? "help" : "";
+	setBodyScrollState();
+}
+
 /******************/
 /* INITIALIZATION */
 /******************/
 			modeSelectorInputReceived();
 		});
 	});
+
+	// Listener for open help button.
+	document.querySelector(".open-help-button").addActivateEvent((event) => {
+		setHelpOverlayVisible(true);
+	});
+	// Listener for close help button.
+	document.querySelector(".help-overlay .close-button").addActivateEvent((event) => {
+		setHelpOverlayVisible(false);
+	});
+
+	// Disable scrolling on the document body, if need be (if help is open).
+	setBodyScrollState();
+
+	// Listener for Escape key (closes the help overlay).
+	document.addEventListener("keyup", (event) => {
+		if (event.keyCode == 27 && location.hash == "#help") {
+			setHelpOverlayVisible(false);
+		}
+	});
 }
 initialize();

popup.js

 	happens until the UI state is updated, killSticky() is called (if needed),
 	and the new settings are saved in storage.)
 
-	What “toggle the current state” actually means depends on the current mode.
+	What "toggle the current state” actually means depends on the current mode.
 
 	[1]	In blacklist mode, toggleState() does one of the following:
 
 
 	// Listener for Options button.
 	document.querySelector("button.options-button").addActivateEvent(() => {
-		chrome.runtime.openOptionsPage(null);
+		window.open(chrome.runtime.getURL('options.html'))
 	});
 	
 	// Listener for the Help button.
 	document.querySelector("button.help-button").addActivateEvent(() => {
-		// TODO: code!
+		window.open(chrome.runtime.getURL('options.html') + "#help");
 	});
 
 	// Listener for reload button (appears when sticky-killing is toggled OFF).