--- a/content_scripts/feed-preview.js	Thu Oct 04 10:16:49 2018 +0200
+++ b/content_scripts/feed-preview.js	Sun Nov 04 09:54:37 2018 +0100
@@ -54,7 +54,7 @@
     return (new XMLSerializer()).serializeToString(parsedDocument);
 }
 
-function nsMapper(prefix) {
+function feedNSResolver(prefix) {
     switch (prefix) {
         case 'atom':
             return 'http://www.w3.org/2005/Atom'
@@ -64,18 +64,18 @@
     return null;
 }
 
-function xpathQuery(doc, scopeElement, xpathQuery, nsMapping) {
-    return doc.evaluate(xpathQuery, scopeElement, nsMapper,
+function feedQueryXPath(feedDocument, scopeElement, xpathQuery) {
+    return feedDocument.evaluate(xpathQuery, scopeElement, feedNSResolver,
             XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue;
 }
 
-function xpathQueryAll(doc, scopeElement, xpathQuery, nsMapping) {
-    let result = doc.evaluate(xpathQuery, scopeElement, nsMapper,
+function feedQueryXPathAll(feedDocument, scopeElement, xpathQuery) {
+    let result = feedDocument.evaluate(xpathQuery, scopeElement, feedNSResolver,
             XPathResult.ORDERED_NODE_ITERATOR_TYPE, null);
     let nodes = [];
     for (let node = result.iterateNext(); node !== null;
             node = result.iterateNext()) {
-            nodes.push(node);
+        nodes.push(node);
     }
 
     return nodes;
@@ -90,7 +90,8 @@
 
 class RSS1Logo extends FeedLogo {
     constructor(feedDocument, imageElement) {
-        let urlElement = xpathQuery(feedDocument, imageElement, './rss:url');
+        let urlElement = feedQueryXPath(feedDocument, imageElement,
+                './rss:url');
         if (urlElement === null) {
             throw new TypeError('missing <url> element in <logo> element');
         }
@@ -100,7 +101,7 @@
         }
         super(url);
 
-        let titleElement = xpathQuery(feedDocument, imageElement,
+        let titleElement = feedQueryXPath(feedDocument, imageElement,
                 './rss:title');
         if (titleElement !== null) {
             this.title = titleElement.textContent.trim();
@@ -110,7 +111,7 @@
 
 class RSS2Logo extends FeedLogo {
     constructor(feedDocument, imageElement) {
-        let urlElement = xpathQuery(feedDocument, imageElement, './url');
+        let urlElement = feedQueryXPath(feedDocument, imageElement, './url');
         if (urlElement === null) {
             throw new TypeError('missing <url> element in <logo> element');
         }
@@ -120,7 +121,8 @@
         }
         super(url);
 
-        let titleElement = xpathQuery(feedDocument, imageElement, './title');
+        let titleElement = feedQueryXPath(feedDocument, imageElement,
+                './title');
         if (titleElement !== null) {
             this.title = titleElement.textContent.trim();
         }
@@ -184,12 +186,14 @@
     constructor(feedDocument, itemElement) {
         super();
 
-        let titleElement = xpathQuery(feedDocument, itemElement, './rss:title');
+        let titleElement = feedQueryXPath(feedDocument, itemElement,
+                './rss:title');
         if (titleElement !== null) {
             this.title = titleElement.textContent;
         }
 
-        let linkElement = xpathQuery(feedDocument, itemElement, './rss:link');
+        let linkElement = feedQueryXPath(feedDocument, itemElement,
+                './rss:link');
         if (linkElement !== null) {
             this.url = parseURL(linkElement.textContent);
         }
@@ -200,29 +204,30 @@
     constructor(feedDocument, itemElement) {
         super();
 
-        let titleElement = xpathQuery(feedDocument, itemElement, './title');
+        let titleElement = feedQueryXPath(feedDocument, itemElement, './title');
         if (titleElement !== null) {
             this.title = titleElement.textContent;
         }
 
-        let linkElement = xpathQuery(feedDocument, itemElement, './link');
+        let linkElement = feedQueryXPath(feedDocument, itemElement, './link');
         if (linkElement !== null) {
             this.url = parseURL(linkElement.textContent);
         }
 
-        let pubDateElement = xpathQuery(feedDocument, itemElement, './pubDate');
+        let pubDateElement = feedQueryXPath(feedDocument, itemElement,
+                './pubDate');
         if (pubDateElement !== null) {
             this.date = parseDate(pubDateElement.textContent);
         }
 
-        let descriptionElement = xpathQuery(feedDocument, itemElement,
+        let descriptionElement = feedQueryXPath(feedDocument, itemElement,
                 './description');
         if (descriptionElement !== null) {
             this.content = normalizeHTML(descriptionElement.textContent.trim());
         }
 
-        for (let enclosureElement of xpathQueryAll(feedDocument, itemElement,
-                './enclosure')) {
+        for (let enclosureElement of
+                feedQueryXPathAll(feedDocument, itemElement, './enclosure')) {
             try {
                 let entryFile = new RSS2EntryFile(enclosureElement);
                 this.files.push(entryFile);
@@ -235,28 +240,28 @@
     constructor(feedDocument, entryElement) {
         super();
 
-        let titleElement = xpathQuery(feedDocument, entryElement,
+        let titleElement = feedQueryXPath(feedDocument, entryElement,
                 './atom:title');
         if (titleElement !== null) {
             this.title = titleElement.textContent.trim();
         }
 
-        let linkElement = xpathQuery(feedDocument, entryElement,
+        let linkElement = feedQueryXPath(feedDocument, entryElement,
                 './atom:link[@href][@rel="alternate"]');
         if (linkElement !== null) {
             this.url = parseURL(linkElement.getAttribute('href'));
         }
 
-        let updatedElement = xpathQuery(feedDocument, entryElement,
+        let updatedElement = feedQueryXPath(feedDocument, entryElement,
                 './atom:updated');
         if (updatedElement !== null) {
             this.date = parseDate(updatedElement.textContent);
         }
 
-        let contentElement = xpathQuery(feedDocument, entryElement,
+        let contentElement = feedQueryXPath(feedDocument, entryElement,
                 './atom:content');
         if (contentElement === null) {
-            contentElement = xpathQuery(feedDocument, entryElement,
+            contentElement = feedQueryXPath(feedDocument, entryElement,
                     './atom:summary');
         }
         if (contentElement !== null) {
@@ -408,19 +413,19 @@
         super();
 
         let documentElement = feedDocument.documentElement;
-        let titleElement = xpathQuery(feedDocument, documentElement,
+        let titleElement = feedQueryXPath(feedDocument, documentElement,
                 './rss:channel/rss:title');
         if (titleElement !== null) {
             this.title = titleElement.textContent;
         }
 
-        let descriptionElement = xpathQuery(feedDocument, documentElement,
+        let descriptionElement = feedQueryXPath(feedDocument, documentElement,
                 './channel/description');
         if (descriptionElement !== null) {
             this.subtitle = descriptionElement.textContent;
         }
 
-        let imageElement = xpathQuery(feedDocument, documentElement,
+        let imageElement = feedQueryXPath(feedDocument, documentElement,
                 './rss:image');
         if (imageElement !== null) {
             try {
@@ -429,7 +434,7 @@
             } catch (e) {}
         }
 
-        let itemElements = xpathQueryAll(feedDocument, documentElement,
+        let itemElements = feedQueryXPathAll(feedDocument, documentElement,
                 './rss:item');
         for (let itemElement of itemElements) {
             let entry = new RSS1Entry(feedDocument, itemElement);
@@ -445,19 +450,19 @@
         super();
 
         let documentElement = feedDocument.documentElement;
-        let titleElement = xpathQuery(feedDocument, documentElement,
+        let titleElement = feedQueryXPath(feedDocument, documentElement,
                 './channel/title');
         if (titleElement !== null) {
             this.title = titleElement.textContent;
         }
 
-        let descriptionElement = xpathQuery(feedDocument, documentElement,
+        let descriptionElement = feedQueryXPath(feedDocument, documentElement,
                 './channel/description');
         if (descriptionElement !== null) {
             this.subtitle = descriptionElement.textContent;
         }
 
-        let imageElement = xpathQuery(feedDocument, documentElement,
+        let imageElement = feedQueryXPath(feedDocument, documentElement,
                 './channel/image');
         if (imageElement !== null) {
             try {
@@ -466,7 +471,7 @@
             } catch (e) {}
         }
 
-        let itemElements = xpathQueryAll(feedDocument, documentElement,
+        let itemElements = feedQueryXPathAll(feedDocument, documentElement,
                 './channel/item');
         for (let itemElement of itemElements) {
             let entry = new RSS2Entry(feedDocument, itemElement);
@@ -482,19 +487,19 @@
         super();
 
         let documentElement = feedDocument.documentElement;
-        let titleElement = xpathQuery(feedDocument, documentElement,
+        let titleElement = feedQueryXPath(feedDocument, documentElement,
                 './atom:title');
         if (titleElement !== null) {
             this.title = titleElement.textContent.trim();
         }
 
-        let subtitleElement = xpathQuery(feedDocument, documentElement,
+        let subtitleElement = feedQueryXPath(feedDocument, documentElement,
                 './atom:subtitle');
         if (subtitleElement !== null) {
             this.subtitle = subtitleElement.textContent.trim();
         }
 
-        let logoElement =  xpathQuery(feedDocument, documentElement,
+        let logoElement =  feedQueryXPath(feedDocument, documentElement,
                 './atom:logo');
         if (logoElement !== null) {
             try {
@@ -503,7 +508,7 @@
             } catch (e) {}
         }
 
-        let entryElements = xpathQueryAll(feedDocument, documentElement,
+        let entryElements = feedQueryXPathAll(feedDocument, documentElement,
                 './atom:entry');
         for (let entryElement of entryElements) {
             this.entries.push(new AtomEntry(feedDocument, entryElement));