diff --git a/.eslintrc b/.eslintrc
index 85e21a98..d02a8b8c 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -12,6 +12,7 @@ globals:
   # messaging.js
   OWN_ORIGIN: false
   KEEP_CHANNEL_OPEN: false
+  RX_SUPPORTED_URLS: false
   configureCommands: false
   notifyAllTabs: false
   refreshAllTabs: false
diff --git a/_locales/en/messages.json b/_locales/en/messages.json
index 9b462ee4..46eb7ae4 100644
--- a/_locales/en/messages.json
+++ b/_locales/en/messages.json
@@ -402,6 +402,20 @@
     "message": "Invalid regexps skipped",
     "description": "RegExp test report: label for the invalid expressions"
   },
+  "styleRegexpPartialExplanation": {
+    "message": "This style uses partially matching regexps in violation of <a href='https://developer.mozilla.org/docs/Web/CSS/@document'>CSS4 @document specification</a> which requires a full URL match. The affected CSS sections were not applied to the page. This style was probably created in Stylish-for-Chrome which incorrectly checks 'regexp()' rules since the very first version (known bug)."
+  },
+  "styleRegexpInvalidExplanation": {
+    "message": "Some 'regexp()' rules that could not be compiled at all."
+  },
+  "styleNotAppliedRegexpProblemTooltip": {
+    "message": "Style was not applied due to its incorrect usage of 'regexp()'",
+    "description": "Tooltip in the popup for styles that were not applied at all"
+  },
+  "styleRegexpProblemTooltip": {
+    "message": "Number of sections not applied due to incorrect usage of 'regexp()'",
+    "description": "Tooltip in the popup for styles that were applied only partially"
+  },
   "styleBeautify": {
     "message": "Beautify",
     "description": "Label for the CSS-beautifier button on the edit style page"
diff --git a/backup/fileSaveLoad.js b/backup/fileSaveLoad.js
index 3bf03510..114d8763 100644
--- a/backup/fileSaveLoad.js
+++ b/backup/fileSaveLoad.js
@@ -70,7 +70,7 @@ function importFromString(jsonString) {
         continue;
       }
       item.name = item.name.trim();
-      const byId = (cachedStyles.byId.get(item.id) || {}).style;
+      const byId = cachedStyles.byId.get(item.id);
       const byName = oldStylesByName.get(item.name);
       const oldStyle = byId && byId.name.trim() == item.name || !byName ? byId : byName;
       if (oldStyle == byName && byName) {
diff --git a/manage.js b/manage.js
index a29855d0..d7094034 100644
--- a/manage.js
+++ b/manage.js
@@ -7,7 +7,7 @@ const TARGET_TYPES = ['domains', 'urls', 'urlPrefixes', 'regexps'];
 const TARGET_LIMIT = 10;
 
 
-getStylesSafe({code: false})
+getStylesSafe()
   .then(showStyles)
   .then(initGlobalEvents);
 
@@ -235,7 +235,7 @@ class EntryOnClick {
   static delete(event) {
     const styleElement = getClickedStyleElement(event);
     const id = styleElement.styleId;
-    const name = ((cachedStyles.byId.get(id) || {}).style || {}).name;
+    const {name} = cachedStyles.byId.get(id) || {};
     animateElement(styleElement, {className: 'highlight'});
     messageBox({
       title: t('deleteStyleConfirm'),
@@ -436,7 +436,7 @@ function searchStyles({immediately, container}) {
   }
 
   for (const element of (container || installed).children) {
-    const {style} = cachedStyles.byId.get(element.styleId) || {};
+    const style = cachedStyles.byId.get(element.styleId) || {};
     if (style) {
       const isMatching = !query
         || isMatchingText(style.name)
diff --git a/messaging.js b/messaging.js
index fb221764..d2e8ecba 100644
--- a/messaging.js
+++ b/messaging.js
@@ -4,6 +4,7 @@
 // keep message channel open for sendResponse in chrome.runtime.onMessage listener
 const KEEP_CHANNEL_OPEN = true;
 const OWN_ORIGIN = chrome.runtime.getURL('');
+const RX_SUPPORTED_URLS = new RegExp(`^(file|https?|ftps?):|^${OWN_ORIGIN}`);
 
 
 function notifyAllTabs(request) {
diff --git a/popup.css b/popup.css
index bcd7c7d6..a92052de 100644
--- a/popup.css
+++ b/popup.css
@@ -1,29 +1,43 @@
 body {
   width: 252px;
   font-size: 12px;
-  font-family: Arial,"Helvetica Neue",Helvetica,sans-serif;
+  font-family: Arial, "Helvetica Neue", Helvetica, sans-serif;
+  margin: 0;
 }
+
+body > div:not(#installed) {
+  margin-left: 0.75em;
+  margin-right: 0.75em;
+}
+
 input[type=checkbox] {
   outline: none;
 }
+
 #disable-all-wrapper {
   padding: 0.3em 0 0.6em;
 }
+
 #no-styles {
   font-style: italic;
 }
+
 #popup-shortcuts-button {
   margin-left: 3px;
 }
+
 .checker {
   display: inline;
 }
+
 .style-name {
   cursor: default;
   font-weight: bold;
   display: block;
 }
-a, a:visited {
+
+a,
+a:visited {
   color: black;
   text-decoration-skip: ink;
 }
@@ -33,53 +47,151 @@ a, a:visited {
   width: 16px;
   vertical-align: top;
 }
+
 .left-gutter input {
   margin-bottom: 1px;
   margin-top: 0;
   margin-left: 0;
 }
+
 .main-controls {
   display: table-cell;
 }
 
-.entry {
-  padding: 0.5em 0;
-}
-.entry:first-child {
-  padding-top: 0;
-}
-
 #unavailable,
 #installed {
   border-bottom: 1px solid black;
   padding-bottom: 2px;
 }
+
 body > DIV:last-of-type,
 body.blocked > DIV {
   border-bottom: none;
 }
+
 #installed {
   padding-top: 2px;
   max-height: 434px;
   overflow-y: auto;
 }
+
 #installed.disabled .style-name {
   text-decoration: line-through;
 }
+
 #installed .actions {
   cursor: default;
 }
+
 #installed .actions a {
   cursor: pointer;
   text-decoration: none;
 }
-#installed .style-edit-link {
+
+/* entry */
+
+.entry {
+  display: flex;
+  align-items: center;
+  padding: 5px 0.75em;
+}
+
+.entry:nth-child(even) {
+  background-color: rgba(0, 0, 0, 0.05);
+}
+
+.entry .style-edit-link {
   margin-right: 2px;
 }
-#installed .style-edit-link, #installed .delete {
+
+.entry .style-edit-link,
+.entry .delete {
   display: inline-block;
   padding: 0 1px 0;
 }
+
+.entry .main-controls {
+  display: flex;
+  flex: 1;
+  width: calc(100% - 20px);
+  align-items: center;
+}
+
+.entry .main-controls label {
+  flex: 1;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  padding-right: 5px;
+}
+
+.not-applied .checker,
+.not-applied .style-name,
+.not-applied .actions > * {
+  opacity: .2;
+  transition: opacity .5s ease-in-out .25s, color .5s ease-in-out .25s;
+}
+
+.not-applied:hover .checker,
+.not-applied:hover .style-name,
+.not-applied:hover .actions > * {
+  opacity: 1;
+}
+
+.not-applied:hover .style-name {
+  color: darkorange;
+}
+
+.regexp-problem-indicator {
+  background-color: darkorange;
+  width: 15px;
+  height: 15px;
+  line-height: 16px;
+  border-radius: 8px;
+  margin-right: 4px;
+  margin-left: 4px;
+  text-align: center;
+  color: white;
+  font-weight: bold;
+  box-sizing: border-box;
+  cursor: pointer;
+}
+
+.regexp-partial .actions,
+.regexp-invalid .actions {
+    order: 2;
+}
+
+#regexp-explanation {
+  position: fixed;
+  background-color: white;
+  left: 0;
+  right: 0;
+  padding: .5rem;
+  font-size: 90%;
+  border-top: 2px solid black;
+  border-bottom: 2px solid black;
+  box-shadow: 0 0 100px black;
+  display: flex;
+  flex-direction: column;
+}
+
+#regexp-explanation > div {
+  display: none;
+  list-style-type: none;
+  padding: 0;
+  margin: 0;
+}
+
+.regexp-partial #regexp-partial,
+.regexp-invalid #regexp-invalid {
+  display: block;
+}
+
+#regexp-explanation > div:not(:last-child) {
+  margin-bottom: .5rem;
+}
+
 .svg-icon {
   pointer-events: none;
   transition: fill .5s;
@@ -92,20 +204,27 @@ body > .actions {
   margin-top: 0.5em;
 }
 
-.actions > div:not(:last-child):not(#disable-all-wrapper), .actions > .main-controls > div:not(:last-child), #unavailable:not(:last-child), #unavailable + .actions {
+.actions > div:not(:last-child):not(#disable-all-wrapper),
+.actions > .main-controls > div:not(:last-child),
+#unavailable:not(:last-child),
+#unavailable + .actions {
   margin-bottom: 0.75em;
 }
-.actions input, .actions label {
+
+.actions input,
+.actions label {
   vertical-align: middle;
 }
 
 #unavailable {
   border: none;
-  display: none; /* flex */
+  display: none;
+  margin-top: 0.75em;
   align-items: center;
   justify-content: center;
   font-size: 14px;
 }
+
 body.blocked #installed,
 body.blocked #find-styles,
 body.blocked #write-style,
@@ -118,41 +237,84 @@ body.blocked #unavailable {
 }
 
 /* Never shown, but can be enabled with a style */
-.enable, .disable {
+
+.enable,
+.disable {
   display: none;
 }
 
 /* 'New style' links */
-#write-style-for {margin-right: .6ex}
-.write-style-link {margin-left: .6ex}
-.write-style-link::before, .write-style-link::after {font-size: 12px}
-.write-style-link::before {content: "\00ad"} /* "soft" hyphen */
-#match {overflow-wrap: break-word;}
+
+#write-style-for {
+  margin-right: .6ex
+}
+
+.write-style-link {
+  margin-left: .6ex
+}
+
+.write-style-link::before,
+.write-style-link::after {
+  font-size: 12px
+}
+
+.write-style-link::before {
+  content: "\00ad"; /* "soft" hyphen */
+}
+
+#match {
+  overflow-wrap: break-word;
+  display: inline-block;
+}
 
 /* "breadcrumbs" 'new style' links */
-.breadcrumbs > .write-style-link {margin-left: 0}
-.breadcrumbs:hover a {color: #bbb; text-decoration: none}
+.breadcrumbs > .write-style-link {
+  margin-left: 0
+}
+
+.breadcrumbs:hover a {
+  color: #bbb;
+  text-decoration: none
+}
+
+/* use just the subdomain name instead of the full domain name */
+.breadcrumbs > .write-style-link[subdomain]:not(:nth-last-child(2)) {
+  font-size: 0
+}
 
-  /* use just the subdomain name instead of the full domain name */
-.breadcrumbs > .write-style-link[subdomain]:not(:nth-last-child(2)) {font-size: 0}
 .breadcrumbs > .write-style-link[subdomain]:not(:nth-last-child(2))::before {
   content: attr(subdomain);
 }
 
-  /* "dot" after each subdomain name */
-.breadcrumbs > .write-style-link[subdomain]::after {content: "."}
-  /* no "dot" after top-level domain */
-.breadcrumbs > .write-style-link:nth-last-child(2)::after {content: none}
-  /* "forward slash" before path ("this URL") */
-.breadcrumbs > .write-style-link:last-child::before {content: "\200b/"}
+/* "dot" after each subdomain name */
+.breadcrumbs > .write-style-link[subdomain]::after {
+  content: "."
+}
+
+/* no "dot" after top-level domain */
+.breadcrumbs > .write-style-link:nth-last-child(2)::after {
+  content: none
+}
+
+/* "forward slash" before path ("this URL") */
+.breadcrumbs > .write-style-link:last-child::before {
+  content: "\200b/"
+}
+
 .breadcrumbs > .write-style-link:last-child:first-child::before,
-.breadcrumbs > .write-style-link[subdomain=""] + .write-style-link::before {content: none}
+.breadcrumbs > .write-style-link[subdomain=""] + .write-style-link::before {
+  content: none
+}
 
-  /* suppress TLD-only link */
-.breadcrumbs > .write-style-link[subdomain=""] {display: none}
+/* suppress TLD-only link */
+.breadcrumbs > .write-style-link[subdomain=""] {
+  display: none
+}
 
-  /* :hover style */
-.breadcrumbs.url\(\) > .write-style-link, /* :hover or :focus on "this URL" sets class="url()" */
+/* :hover style */
+.breadcrumbs.url\(\) > .write-style-link,
+
+/* :hover or :focus on "this URL" sets class="url()" */
 .breadcrumbs > .write-style-link:hover,
 .breadcrumbs > .write-style-link:focus,
 .breadcrumbs > .write-style-link:hover ~ .write-style-link[subdomain],
@@ -162,13 +324,15 @@ body.blocked #unavailable {
   text-decoration-skip: ink;
 }
 
-  /* action buttons */
+/* action buttons */
+
 #popup-options {
   display: flex;
   flex-direction: row;
   justify-content: space-around;
   padding: 1.2em 0;
 }
+
 #popup-options button {
   margin: 0 2px;
   width: 33%;
@@ -177,72 +341,43 @@ body.blocked #unavailable {
   text-overflow: ellipsis;
 }
 
-  /* margins */
-body {
-  margin: 0;
-}
-body>div:not(#installed) {
-  margin-left:0.75em;
-  margin-right:0.75em;
-}
-#unavailable {
-  margin-top: 0.75em;
-}
-#installed .entry {
-}
-  /* entries */
-#installed .entry {
-  display: flex;
-  align-items: center;
-  padding: 5px 0.75em;
-}
-#installed .entry:nth-child(even) {
-  background-color: rgba(0, 0, 0, 0.05);
-}
-#installed .main-controls {
-  display: flex;
-  flex: 1;
-  width: calc(100% - 20px);
-  align-items: center;
-}
-#installed .main-controls label {
-  flex: 1;
-  overflow: hidden;
-  text-overflow: ellipsis;
-  white-space: nowrap;
-  padding-right: 5px;
-}
-  /* confirm */
+/* confirm */
+
 #confirm,
-#confirm>div>span {
+#confirm > div > span {
   align-items: center;
   justify-content: center;
 }
+
 #confirm {
   z-index: 2147483647;
-  display: none; /* flex */
+  display: none;
   position: absolute;
   left: 0;
   top: 0;
   width: 100%;
   height: 100%;
-  margin:  0!important;
+  margin: 0 !important;
   box-sizing: border-box;
   background-color: rgba(0, 0, 0, 0.4);
   animation: lights-off .5s cubic-bezier(.03, .67, .08, .94);
   animation-fill-mode: both;
 }
+
 #confirm.lights-on {
   animation: lights-on .25s ease-in-out;
   animation-fill-mode: both;
 }
-#confirm.lights-on > div{
+
+#confirm.lights-on > div {
   display: none;
 }
+
 #confirm[data-display=true] {
   display: flex;
 }
-#confirm>div {
+
+#confirm > div {
   width: 80%;
   height: 100px;
   max-height: 80%;
@@ -252,25 +387,30 @@ body>div:not(#installed) {
   flex-direction: column;
   border: solid 2px rgba(0, 0, 0, 0.5);
 }
-#confirm>div>span {
+
+#confirm > div > span {
   display: flex;
   flex: 1;
   padding: 0 10px;
 }
-#confirm>div>b {
+
+#confirm > div > b {
   padding: 10px;
   white-space: nowrap;
   overflow: hidden;
   text-overflow: ellipsis;
 }
-#confirm>div>div {
+
+#confirm > div > div {
   padding: 10px;
   text-align: center;
 }
-.non-windows #confirm>div>div {
+
+.non-windows #confirm > div > div {
   direction: rtl;
   text-align: right;
 }
+
 @keyframes lights-off {
   from {
     background-color: transparent;
@@ -279,6 +419,7 @@ body>div:not(#installed) {
     background-color: rgba(0, 0, 0, 0.4);
   }
 }
+
 @keyframes lights-on {
   from {
     background-color: rgba(0, 0, 0, 0.4);
@@ -287,4 +428,3 @@ body>div:not(#installed) {
     background-color: transparent;
   }
 }
-
diff --git a/popup.html b/popup.html
index 5fb3f9b6..0a36c1ad 100644
--- a/popup.html
+++ b/popup.html
@@ -37,7 +37,19 @@
         <div id="no-styles" class="entry" i18n-text="noStylesForSite"></div>
     </template>
 
-    <script src="localization.js"></script>
+    <template data-id="regexpProblemIndicator">
+      <div class="regexp-problem-indicator" i18n-title="styleRegexpProblemTooltip"></div>
+    </template>
+
+    <template data-id="regexpProblemExplanation">
+      <div id="regexp-explanation">
+        <div id="regexp-partial" i18n-html="styleRegexpPartialExplanation"></div>
+        <div id="regexp-invalid" i18n-text="styleRegexpInvalidExplanation"></div>
+        <button i18n-text="confirmOK"></button>
+      </div>
+    </template>
+
+  <script src="localization.js"></script>
     <script src="health.js"></script>
     <script src="storage.js"></script>
     <script src="messaging.js"></script>
@@ -81,7 +93,7 @@
                 <a id="find-styles-link" href="#" i18n-text="findStylesForSite"></a>
             </div>
             <div id="write-style">
-                <span id="write-style-for" i18n-text="writeStyleFor"><br></span>
+                <span id="write-style-for" i18n-text="writeStyleFor"></span>
             </div>
         </div>
     <!-- Actions -->
diff --git a/popup.js b/popup.js
index 23f6a30f..553d3ab3 100644
--- a/popup.js
+++ b/popup.js
@@ -1,15 +1,19 @@
+/* global SLOPPY_REGEXP_PREFIX, compileStyleRegExps */
 'use strict';
 
 let installed;
+let tabURL;
 
 getActiveTabRealURL().then(url => {
-  const RX_SUPPORTED_URLS = new RegExp(`^(file|https?|ftps?):|^${OWN_ORIGIN}`);
-  const isUrlSupported = RX_SUPPORTED_URLS.test(url);
+  tabURL = RX_SUPPORTED_URLS.test(url) ? url : '';
   Promise.all([
-    isUrlSupported ? getStylesSafe({matchUrl: url}) : null,
-    onDOMready().then(() => initPopup(isUrlSupported ? url : '')),
-  ])
-    .then(([styles]) => styles && showStyles(styles));
+    tabURL && getStylesSafe({matchUrl: tabURL}),
+    onDOMready().then(() => {
+      initPopup(tabURL);
+    }),
+  ]).then(([styles]) => {
+    showStyles(styles);
+  });
 });
 
 
@@ -116,30 +120,55 @@ function initPopup(url) {
 
 
 function showStyles(styles) {
+  if (!styles) {
+    return;
+  }
   if (!styles.length) {
     installed.innerHTML = template.noStyles.outerHTML;
-  } else {
-    const enabledFirst = prefs.get('popup.enabledFirst');
-    styles.sort((a, b) => (
-      enabledFirst && a.enabled !== b.enabled
-        ? !(a.enabled < b.enabled) ? -1 : 1
-        : a.name.localeCompare(b.name)
-    ));
-    const fragment = document.createDocumentFragment();
-    for (const style of styles) {
-      fragment.appendChild(createStyleElement(style));
-    }
-    installed.appendChild(fragment);
+    return;
   }
+
+  const enabledFirst = prefs.get('popup.enabledFirst');
+  styles.sort((a, b) => (
+    enabledFirst && a.enabled !== b.enabled
+      ? !(a.enabled < b.enabled) ? -1 : 1
+      : a.name.localeCompare(b.name)
+  ));
+
+  let postponeDetect = false;
+  const t0 = performance.now();
+  const container = document.createDocumentFragment();
+  for (const style of styles) {
+    createStyleElement({style, container, postponeDetect});
+    postponeDetect = postponeDetect || performance.now() - t0 > 100;
+  }
+  installed.appendChild(container);
+
+  getStylesSafe({matchUrl: tabURL, strictRegexp: false})
+    .then(unscreenedStyles => {
+      for (const unscreened of unscreenedStyles) {
+        if (!styles.includes(unscreened)) {
+          postponeDetect = postponeDetect || performance.now() - t0 > 100;
+          createStyleElement({
+            style: Object.assign({appliedSections: [], postponeDetect}, unscreened),
+          });
+        }
+      }
+    });
 }
 
 
 // silence the inapplicable warning for async code
 /* eslint no-use-before-define: [2, {"functions": false, "classes": false}] */
-function createStyleElement(style) {
+function createStyleElement({
+  style,
+  container = installed,
+  postponeDetect,
+}) {
   const entry = template.style.cloneNode(true);
   entry.setAttribute('style-id', style.id);
   Object.assign(entry, {
+    id: 'style-' + style.id,
     styleId: style.id,
     className: entry.className + ' ' + (style.enabled ? 'enabled' : 'disabled'),
     onmousedown: openEditorOnMiddleclick,
@@ -171,7 +200,18 @@ function createStyleElement(style) {
   $('.disable', entry).onclick = EntryOnClick.toggle;
   $('.delete', entry).onclick = EntryOnClick.delete;
 
-  return entry;
+  if (postponeDetect) {
+    setTimeout(detectSloppyRegexps, 0, {entry, style});
+  } else {
+    detectSloppyRegexps({entry, style});
+  }
+
+  const oldElement = $('#style-' + style.id);
+  if (oldElement) {
+    oldElement.parentNode.replaceChild(entry, oldElement);
+  } else {
+    container.appendChild(entry);
+  }
 }
 
 
@@ -194,7 +234,7 @@ class EntryOnClick {
     const box = $('#confirm');
     box.dataset.display = true;
     box.style.cssText = '';
-    $('b', box).textContent = ((cachedStyles.byId.get(id) || {}).style || {}).name;
+    $('b', box).textContent = (cachedStyles.byId.get(id) || {}).name;
     $('[data-cmd="ok"]', box).onclick = () => confirm(true);
     $('[data-cmd="cancel"]', box).onclick = () => confirm(false);
     window.onkeydown = event => {
@@ -219,6 +259,18 @@ class EntryOnClick {
     }
   }
 
+  static indicator(event) {
+    const entry = getClickedStyleElement(event);
+    const info = template.regexpProblemExplanation.cloneNode(true);
+    $$('#' + info.id).forEach(el => el.remove());
+    $$('a', info).forEach(el => (el.onclick = openURLandHide));
+    $$('button', info).forEach(el => (el.onclick = EntryOnClick.closeExplanation));
+    entry.appendChild(info);
+  }
+
+  static closeExplanation(event) {
+    $('#regexp-explanation').remove();
+  }
 }
 
 
@@ -264,24 +316,51 @@ function openURLandHide(event) {
 
 
 function handleUpdate(style) {
-  const styleElement = $(`[style-id="${style.id}"]`, installed);
-  if (styleElement) {
-    installed.replaceChild(createStyleElement(style), styleElement);
-  } else {
-    getActiveTabRealURL().then(url => {
-      if (getApplicableSections(style, url).length) {
-        // a new style for the current url is installed
-        $('#unavailable').style.display = 'none';
-        installed.appendChild(createStyleElement(style));
-      }
-    });
+  if ($('#style-' + style.id)) {
+    createStyleElement({style});
+    return;
+  }
+  // Add an entry when a new style for the current url is installed
+  if (tabURL && getApplicableSections({style, matchUrl: tabURL, stopOnFirst: true}).length) {
+    $('#unavailable').style.display = 'none';
+    createStyleElement({style});
   }
 }
 
 
 function handleDelete(id) {
-  const styleElement = $(`[style-id="${id}"]`, installed);
-  if (styleElement) {
-    installed.removeChild(styleElement);
+  $$('#style-' + id).forEach(el => el.remove());
+}
+
+
+/*
+  According to CSS4 @document specification the entire URL must match.
+  Stylish-for-Chrome implemented it incorrectly since the very beginning.
+  We'll detect styles that abuse the bug by finding the sections that
+  would have been applied by Stylish but not by us as we follow the spec.
+  Additionally we'll check for invalid regexps.
+*/
+function detectSloppyRegexps({entry, style}) {
+  const {
+    appliedSections = getApplicableSections({style, matchUrl: tabURL}),
+    wannabeSections = getApplicableSections({style, matchUrl: tabURL, strictRegexp: false}),
+  } = style;
+
+  compileStyleRegExps({style, compileAll: true});
+  entry.hasInvalidRegexps = wannabeSections.some(section =>
+    section.regexps.some(rx => !cachedStyles.regexps.has(rx)));
+  entry.sectionsSkipped = wannabeSections.length - appliedSections.length;
+
+  if (!appliedSections.length) {
+    entry.classList.add('not-applied');
+    $('.style-name', entry).title = t('styleNotAppliedRegexpProblemTooltip');
+  }
+  if (entry.sectionsSkipped || entry.hasInvalidRegexps) {
+    entry.classList.toggle('regexp-partial', entry.sectionsSkipped);
+    entry.classList.toggle('regexp-invalid', entry.hasInvalidRegexps);
+    const indicator = template.regexpProblemIndicator.cloneNode(true);
+    indicator.appendChild(document.createTextNode(entry.sectionsSkipped || '!'));
+    indicator.onclick = EntryOnClick.indicator;
+    $('.main-controls', entry).appendChild(indicator);
   }
 }
diff --git a/storage.js b/storage.js
index 3f3c3e33..656fcbf0 100644
--- a/storage.js
+++ b/storage.js
@@ -28,7 +28,7 @@ const RX_NAMESPACE = new RegExp([/[\s\r\n]*/,
   /(@namespace[\s\r\n]+(?:[^\s\r\n]+[\s\r\n]+)?url\(http:\/\/.*?\);)/,
   /[\s\r\n]*/].map(rx => rx.source).join(''), 'g');
 const RX_CSS_COMMENTS = /\/\*[\s\S]*?\*\//g;
-
+const SLOPPY_REGEXP_PREFIX = '\0';
 
 // Let manage/popup/edit reuse background page variables
 // Note, only 'var'-declared variables are visible from another extension page
@@ -39,11 +39,11 @@ var cachedStyles, prefs;
   cachedStyles = bg && bg.cachedStyles || {
     bg,
     list: null,
-    noCode: null,
     byId: new Map(),
     filters: new Map(),
     regexps: new Map(),
     urlDomains: new Map(),
+    emptyCode: new Map(), // entire code is comments/whitespace/@namespace
     mutex: {
       inProgress: false,
       onDone: [],
@@ -89,15 +89,12 @@ function getStyles(options, callback) {
     const os = tx.objectStore('styles');
     os.getAll().onsuccess = event => {
       cachedStyles.list = event.target.result || [];
-      cachedStyles.noCode = [];
       cachedStyles.byId.clear();
       for (const style of cachedStyles.list) {
-        const noCode = getStyleWithNoCode(style);
-        cachedStyles.noCode.push(noCode);
-        cachedStyles.byId.set(style.id, {style, noCode});
-        compileStyleRegExps(style);
+        cachedStyles.byId.set(style.id, style);
+        compileStyleRegExps({style});
       }
-      //console.log('%s getStyles %s, invoking cached callbacks: %o', (performance.now() - t0).toFixed(1), JSON.stringify(options), cachedStyles.mutex.onDone.map(e => JSON.stringify(e.options)))
+      //console.debug('%s getStyles %s, invoking cached callbacks: %o', (performance.now() - t0).toFixed(1), JSON.stringify(options), cachedStyles.mutex.onDone.map(e => JSON.stringify(e.options))); // eslint-disable-line max-len
       callback(filterStyles(options));
 
       cachedStyles.mutex.inProgress = false;
@@ -134,19 +131,16 @@ function invalidateCache(andNotify, {added, updated, deletedId} = {}) {
   if (updated) {
     const cached = cachedStyles.byId.get(updated.id);
     if (cached) {
-      Object.assign(cached.style, updated);
-      Object.assign(cached.noCode, getStyleWithNoCode(updated));
-      //console.log('cache: updated', updated);
+      Object.assign(cached, updated);
+      //console.debug('cache: updated', updated);
     }
     cachedStyles.filters.clear();
     return;
   }
   if (added) {
-    const noCode = getStyleWithNoCode(added);
     cachedStyles.list.push(added);
-    cachedStyles.noCode.push(noCode);
-    cachedStyles.byId.set(added.id, {style: added, noCode});
-    //console.log('cache: added', added);
+    cachedStyles.byId.set(added.id, added);
+    //console.debug('cache: added', added);
     cachedStyles.filters.clear();
     return;
   }
@@ -155,46 +149,47 @@ function invalidateCache(andNotify, {added, updated, deletedId} = {}) {
     if (deletedStyle) {
       const cachedIndex = cachedStyles.list.indexOf(deletedStyle);
       cachedStyles.list.splice(cachedIndex, 1);
-      cachedStyles.noCode.splice(cachedIndex, 1);
       cachedStyles.byId.delete(deletedId);
-      //console.log('cache: deleted', deletedStyle);
+      //console.debug('cache: deleted', deletedStyle);
       cachedStyles.filters.clear();
       return;
     }
   }
   cachedStyles.list = null;
-  cachedStyles.noCode = null;
-  //console.log('cache cleared');
+  //console.debug('cache cleared');
   cachedStyles.filters.clear();
 }
 
 
-function filterStyles(options = {}) {
+function filterStyles({
+  enabled,
+  url = null,
+  id = null,
+  matchUrl = null,
+  asHash = null,
+  strictRegexp = true, // used by the popup to detect bad regexps
+} = {}) {
   //const t0 = performance.now();
-  const enabled = fixBoolean(options.enabled);
-  const url = 'url' in options ? options.url : null;
-  const id = 'id' in options ? Number(options.id) : null;
-  const matchUrl = 'matchUrl' in options ? options.matchUrl : null;
-  const code = 'code' in options ? options.code : true;
-  const asHash = 'asHash' in options ? options.asHash : false;
+  enabled = fixBoolean(enabled);
+  id = id === null ? null : Number(id);
 
   if (enabled === null
     && url === null
     && id === null
     && matchUrl === null
     && asHash != true) {
-    //console.log('%c%s filterStyles SKIPPED LOOP %s', 'color:gray', (performance.now() - t0).toFixed(1), JSON.stringify(options))
-    return code ? cachedStyles.list : cachedStyles.noCode;
+    //console.debug('%c%s filterStyles SKIPPED LOOP %s', 'color:gray', (performance.now() - t0).toFixed(1), enabled, id, asHash, strictRegexp, matchUrl); // eslint-disable-line max-len
+    return cachedStyles.list;
   }
   // silence the inapplicable warning for async code
   // eslint-disable-next-line no-use-before-define
   const disableAll = asHash && prefs.get('disableAll', false);
 
   // add \t after url to prevent collisions (not sure it can actually happen though)
-  const cacheKey = ' ' + enabled + url + '\t' + id + matchUrl + '\t' + code + asHash;
+  const cacheKey = ' ' + enabled + url + '\t' + id + matchUrl + '\t' + asHash + strictRegexp;
   const cached = cachedStyles.filters.get(cacheKey);
   if (cached) {
-    //console.log('%c%s filterStyles REUSED RESPONSE %s', 'color:gray', (performance.now() - t0).toFixed(1), JSON.stringify(options))
+    //console.debug('%c%s filterStyles REUSED RESPONSE %s', 'color:gray', (performance.now() - t0).toFixed(1), enabled, id, asHash, strictRegexp, matchUrl); // eslint-disable-line max-len
     cached.hits++;
     cached.lastHit = Date.now();
 
@@ -212,19 +207,22 @@ function filterStyles(options = {}) {
   }
 
   const styles = id === null
-    ? (code ? cachedStyles.list : cachedStyles.noCode)
-    : [(cachedStyles.byId.get(id) || {})[code ? 'style' : 'noCode']];
+    ? cachedStyles.list
+    : [cachedStyles.byId.get(id)];
   const filtered = asHash ? {} : [];
   if (!styles) {
     // may happen when users [accidentally] reopen an old URL
     // of edit.html with a non-existent style id parameter
     return filtered;
   }
+  const needSections = asHash || matchUrl !== null;
+
   for (let i = 0, style; (style = styles[i]); i++) {
     if ((enabled === null || style.enabled == enabled)
       && (url === null || style.url == url)
       && (id === null || style.id == id)) {
-      const sections = (asHash || matchUrl !== null) && getApplicableSections(style, matchUrl);
+      const sections = needSections &&
+        getApplicableSections({style, matchUrl, strictRegexp, stopOnFirst: !asHash});
       if (asHash) {
         if (sections.length) {
           filtered[style.id] = sections;
@@ -234,7 +232,7 @@ function filterStyles(options = {}) {
       }
     }
   }
-  //console.log('%s filterStyles %s', (performance.now() - t0).toFixed(1), JSON.stringify(options))
+  //console.debug('%s filterStyles %s', (performance.now() - t0).toFixed(1), enabled, id, asHash, strictRegexp, matchUrl); // eslint-disable-line max-len
   cachedStyles.filters.set(cacheKey, {
     styles: filtered,
     lastHit: Date.now(),
@@ -307,7 +305,7 @@ function saveStyle(style) {
           os.put(style).onsuccess = eventPut => {
             style.id = style.id || eventPut.target.result;
             invalidateCache(notify, existed ? {updated: style} : {added: style});
-            compileStyleRegExps(style);
+            compileStyleRegExps({style});
             if (notify) {
               notifyAllTabs({
                 method: existed ? 'styleUpdated' : 'styleAdded',
@@ -338,7 +336,7 @@ function saveStyle(style) {
         // Give it the ID that was generated
         style.id = event.target.result;
         invalidateCache(notify, {added: style});
-        compileStyleRegExps(style);
+        compileStyleRegExps({style});
         if (notify) {
           notifyAllTabs({method: 'styleAdded', style, reason});
         }
@@ -434,68 +432,88 @@ function getType(o) {
 }
 
 
-function getApplicableSections(style, url) {
+function getApplicableSections({style, matchUrl, strictRegexp = true, stopOnFirst}) {
+  //let t0 = 0;
   const sections = [];
   checkingSections:
   for (const section of style.sections) {
-    // only http, https, file, ftp, and chrome-extension://OWN_EXTENSION_ID allowed
-    if (!url.startsWith('http')
-      && !url.startsWith('ftp')
-      && !url.startsWith('file')
-      && !url.startsWith(OWN_ORIGIN)) {
-      continue checkingSections;
-    }
-    if (section.urls.length == 0
-    && section.domains.length == 0
-    && section.urlPrefixes.length == 0
-    && section.regexps.length == 0) {
-      sections.push(section);
-      continue checkingSections;
-    }
-    if (section.urls.indexOf(url) != -1) {
-      sections.push(section);
-      continue checkingSections;
-    }
-    for (const urlPrefix of section.urlPrefixes) {
-      if (url.startsWith(urlPrefix)) {
-        sections.push(section);
+    andCollect:
+    do {
+      // only http, https, file, ftp, and chrome-extension://OWN_EXTENSION_ID allowed
+      if (!matchUrl.startsWith('http')
+        && !matchUrl.startsWith('ftp')
+        && !matchUrl.startsWith('file')
+        && !matchUrl.startsWith(OWN_ORIGIN)) {
         continue checkingSections;
       }
-    }
-    const urlDomains = cachedStyles.urlDomains.get(url) || getDomains(url);
-    for (const domain of urlDomains) {
-      if (section.domains.indexOf(domain) != -1) {
-        sections.push(section);
-        continue checkingSections;
+      if (section.urls.length == 0
+      && section.domains.length == 0
+      && section.urlPrefixes.length == 0
+      && section.regexps.length == 0) {
+        break andCollect;
       }
-    }
-    for (const regexp of section.regexps) {
-      let rx = cachedStyles.regexps.get(regexp);
-      if (rx == false) {
-        // bad regexp
-        continue;
+      if (section.urls.indexOf(matchUrl) != -1) {
+        break andCollect;
       }
-      if (!rx) {
-        rx = tryRegExp('^(?:' + regexp + ')$');
-        cachedStyles.regexps.set(regexp, rx || false);
-        if (!rx) {
-          // bad regexp
-          continue;
+      for (const urlPrefix of section.urlPrefixes) {
+        if (matchUrl.startsWith(urlPrefix)) {
+          break andCollect;
         }
       }
-      if (rx.test(url)) {
-        sections.push(section);
-        continue checkingSections;
+      if (section.domains.length) {
+        const urlDomains = cachedStyles.urlDomains.get(matchUrl) || getDomains(matchUrl);
+        for (const domain of urlDomains) {
+          if (section.domains.indexOf(domain) != -1) {
+            break andCollect;
+          }
+        }
+      }
+      for (const regexp of section.regexps) {
+        for (let pass = 1; pass <= (strictRegexp ? 1 : 2); pass++) {
+          const cacheKey = pass == 1 ? regexp : SLOPPY_REGEXP_PREFIX + regexp;
+          let rx = cachedStyles.regexps.get(cacheKey);
+          if (rx == false) {
+            // invalid regexp
+            break;
+          }
+          if (!rx) {
+            const anchored = pass == 1 ? '^(?:' + regexp + ')$' : '^' + regexp + '$';
+            rx = tryRegExp(anchored);
+            cachedStyles.regexps.set(cacheKey, rx || false);
+            if (!rx) {
+              // invalid regexp
+              break;
+            }
+          }
+          if (rx.test(matchUrl)) {
+            break andCollect;
+          }
+        }
+      }
+      continue checkingSections;
+    } while (0);
+    // Collect the section if not empty or namespace-only.
+    // We don't check long code as it's slow both for emptyCode declared as Object
+    // and as Map in case the string is not the same reference used to add the item
+    //const t0start = performance.now();
+    const code = section.code;
+    let isEmpty = code.length < 1000 && cachedStyles.emptyCode.get(code);
+    if (isEmpty === undefined) {
+      isEmpty = !code || !code.trim()
+        || code.indexOf('@namespace') >= 0
+        && code.replace(RX_CSS_COMMENTS, '').replace(RX_NAMESPACE, '').trim() == '';
+      cachedStyles.emptyCode.set(code, isEmpty);
+    }
+    //t0 += performance.now() - t0start;
+    if (!isEmpty) {
+      sections.push(section);
+      if (stopOnFirst) {
+        //t0 >= 0.1 && console.debug('%s emptyCode', t0.toFixed(1)); // eslint-disable-line no-unused-expressions
+        return sections;
       }
     }
   }
-  // ignore @namespace-only results
-  if (sections.length == 1
-  && sections[0].code
-  && sections[0].code.indexOf('@namespace') >= 0
-  && sections[0].code.replace(RX_CSS_COMMENTS, '').replace(RX_NAMESPACE, '').trim() == '') {
-    return [];
-  }
+  //t0 >= 0.1 && console.debug('%s emptyCode', t0.toFixed(1)); // eslint-disable-line no-unused-expressions
   return sections;
 }
 
@@ -888,18 +906,22 @@ function styleSectionsEqual(styleA, styleB) {
 }
 
 
-function compileStyleRegExps(style) {
+function compileStyleRegExps({style, compileAll}) {
   const t0 = performance.now();
   for (const section of style.sections || []) {
     for (const regexp of section.regexps) {
-      // we want to match the full url, so add ^ and $ if not already present
-      if (cachedStyles.regexps.has(regexp)) {
-        continue;
-      }
-      const rx = tryRegExp('^(?:' + regexp + ')$');
-      cachedStyles.regexps.set(regexp, rx || false);
-      if (performance.now() - t0 > 100) {
-        return;
+      for (let pass = 1; pass <= (compileAll ? 2 : 1); pass++) {
+        const cacheKey = pass == 1 ? regexp : SLOPPY_REGEXP_PREFIX + regexp;
+        if (cachedStyles.regexps.has(cacheKey)) {
+          continue;
+        }
+        // according to CSS4 @document specification the entire URL must match
+        const anchored = pass == 1 ? '^(?:' + regexp + ')$' : '^' + regexp + '$';
+        const rx = tryRegExp(anchored);
+        cachedStyles.regexps.set(cacheKey, rx || false);
+        if (!compileAll && performance.now() - t0 > 100) {
+          return;
+        }
       }
     }
   }