diff -u b/core/misc/ajax.es6.js b/core/misc/ajax.es6.js
--- b/core/misc/ajax.es6.js
+++ b/core/misc/ajax.es6.js
@@ -1020,68 +1020,8 @@
       // Apply any settings from the returned JSON if available.
       const settings = response.settings || ajax.settings || drupalSettings;
 
-      // We don't know what response.data contains: it might be a string of text
-      // without HTML, so don't rely on jQuery correctly interpreting
-      // $(response.data) as new HTML rather than a CSS selector. Also, if
-      // response.data contains top-level text nodes, they get lost with either
-      // $(response.data) or $('<div></div>').replaceWith(response.data).
-      // attachBehaviors() can, for the same reason, not be called with a
-      // context object that includes top-level text nodes. Therefore text nodes
-      // will be wrapped with a <span> element. This also gives themers the
-      // possibility to style the response.
-      let $newContent;
-      // We use the trimmed data to be able to detect cases when the response
-      // has only top-level elements or comment nodes with extra whitespace
-      // around. In that case whitespaces are removed and the response
-      // should not be wrapped.
-      // For example:
-      //   '  <div>content</div> ' is equivalent to '<div>content</div>' and
-      // no extra wrapper will be added.
-      const trimmedData = response.data.trim();
-      // List of DOM nodes contained in the response for processing.
-      let responseDataNodes;
-
-      // When 'data' is empty or is only whitespace, manually create the node
-      // array because parseHTML would return null.
-      if (trimmedData === '') {
-        responseDataNodes = [document.createTextNode(response.data)];
-      }
-      else {
-        responseDataNodes = $.parseHTML(trimmedData, true);
-      }
-      // Check every node for it's type to decide if wrapping is necessary.
-      const onlyElementNodes = responseDataNodes.every(
-        element => element.nodeType === Node.ELEMENT_NODE
-          || element.nodeType === Node.COMMENT_NODE
-          // Ignore any TEXT_NODE that only contains whitespace.
-          || (element.nodeType === Node.TEXT_NODE && element.textContent.trim().length === 0),
-      );
-      // Find the first node that is not COMMENT_NODE.
-      const firstNonCommentNode = responseDataNodes.filter(element => element.nodeType !== Node.COMMENT_NODE)[0];
-
-      // When there are only element and/or comment nodes in the response or if
-      // the method is 'html' and the element can be safely converted a jQuery
-      // object, no extra wrapping necessary.
-      if (onlyElementNodes || (method === 'html' && firstNonCommentNode.nodeType === Node.ELEMENT_NODE)) {
-        $newContent = $(trimmedData);
-      }
-      // When there are other types of top-level nodes, the response needs to be
-      // wrapped.
-      else {
-        const onlyTextOrCommentNodes = responseDataNodes.every(
-          element => element.nodeType === Node.COMMENT_NODE || element.nodeType === Node.TEXT_NODE,
-        );
-        // If response.data contains only nodes of the type TEXT_NODE or
-        // COMMENT_NODE, response.data will be wrapped with SPAN.
-        if (onlyTextOrCommentNodes) {
-          $newContent = $('<span></span>');
-        }
-        else {
-          $newContent = $('<div></div>');
-        }
-        // Use response.data to keep whitespace as-is.
-        $newContent.html(response.data);
-      }
+      // Parse response.data into an element collection.
+      const $newContent = $($.parseHTML(response.data));
 
       // If removing content from the wrapper, detach behaviors first.
       switch (method) {
diff -u b/core/misc/ajax.js b/core/misc/ajax.js
--- b/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -481,41 +481,7 @@
 
       var settings = response.settings || ajax.settings || drupalSettings;
 
-      var $newContent = void 0;
-
-      var trimmedData = response.data.trim();
-
-      var responseDataNodes = void 0;
-
-      if (trimmedData === '') {
-        responseDataNodes = [document.createTextNode(response.data)];
-      } else {
-        responseDataNodes = $.parseHTML(trimmedData, true);
-      }
-
-      var onlyElementNodes = responseDataNodes.every(function (element) {
-        return element.nodeType === Node.ELEMENT_NODE || element.nodeType === Node.COMMENT_NODE || element.nodeType === Node.TEXT_NODE && element.textContent.trim().length === 0;
-      });
-
-      var firstNonCommentNode = responseDataNodes.filter(function (element) {
-        return element.nodeType !== Node.COMMENT_NODE;
-      })[0];
-
-      if (onlyElementNodes || method === 'html' && firstNonCommentNode.nodeType === Node.ELEMENT_NODE) {
-        $newContent = $(trimmedData);
-      } else {
-          var onlyTextOrCommentNodes = responseDataNodes.every(function (element) {
-            return element.nodeType === Node.COMMENT_NODE || element.nodeType === Node.TEXT_NODE;
-          });
-
-          if (onlyTextOrCommentNodes) {
-            $newContent = $('<span></span>');
-          } else {
-            $newContent = $('<div></div>');
-          }
-
-          $newContent.html(response.data);
-        }
+      var $newContent = $($.parseHTML(response.data));
 
       switch (method) {
         case 'html':