2 files changed, 36 insertions, 4 deletions
diff --git a/guides/source/testing.md b/guides/source/testing.md
index 3e12afc000..2ecd560a87 100644
--- a/guides/source/testing.md
+++ b/guides/source/testing.md
@@ -605,13 +605,13 @@ end
 
 Testing the response to your request by asserting the presence of key HTML elements and their content is a useful way to test the views of your application. The `assert_select` assertion allows you to do this by using a simple yet powerful syntax.
 
-NOTE: You may find references to `assert_tag` in other documentation, but this is now deprecated in favor of `assert_select`.
+NOTE: You may find references to `assert_tag` in other documentation. This has been removed in 4.2. Use `assert_select` instead.
 
 There are two forms of `assert_select`:
 
-`assert_select(selector, [equality], [message])` ensures that the equality condition is met on the selected elements through the selector. The selector may be a CSS selector expression (String), an expression with substitution values, or an `HTML::Selector` object.
+`assert_select(selector, [equality], [message])` ensures that the equality condition is met on the selected elements through the selector. The selector may be a CSS selector expression (String) or an expression with substitution values.
 
-`assert_select(element, selector, [equality], [message])` ensures that the equality condition is met on all the selected elements through the selector starting from the _element_ (instance of `HTML::Node`) and its descendants.
+`assert_select(element, selector, [equality], [message])` ensures that the equality condition is met on all the selected elements through the selector starting from the _element_ (instance of `Nokogiri::XML::Node` or `Nokogiri::XML::NodeSet`) and its descendants.
 
 For example, you could verify the contents on the title element in your response with:
 
@@ -641,7 +641,7 @@ assert_select "ol" do
 end
 ```
 
-The `assert_select` assertion is quite powerful. For more advanced usage, refer to its [documentation](http://api.rubyonrails.org/classes/ActionDispatch/Assertions/SelectorAssertions.html).
+The `assert_select` assertion is quite powerful. For more advanced usage, refer to its [documentation](https://github.com/rails/rails-dom-testing/blob/master/lib/rails/dom/testing/assertions/selector_assertions.rb).
 
 #### Additional View-Based Assertions
 
diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index cc20782780..799d5f3bc9 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -91,6 +91,38 @@ after_bundle do
 end
 ```
 
+### Rails Html Sanitizer
+
+There's a new choice for sanitizing HTML fragments in your applications. The
+venerable html-scanner approach is now officially being deprecated in favor of
+[`Rails Html Sanitizer`](https://github.com/rails/rails-html-sanitizer).
+
+This means the methods `sanitize`, `sanitize_css`, `strip_tags` and
+`strip_links` are backed by a new implementation.
+
+In the next major Rails version `Rails Html Sanitizer` will be the default
+sanitizer. It already is for new applications.
+
+Include this in your Gemfile to try it out today:
+
+```ruby
+gem 'rails-html-sanitizer'
+```
+
+This new sanitizer uses [Loofah](https://github.com/flavorjones/loofah) internally. Loofah in turn uses Nokogiri, which
+wraps XML parsers written in both C and Java, so sanitization should be faster
+no matter which Ruby version you run.
+
+The new version updates `sanitize`, so it can take a `Loofah::Scrubber` for
+powerful scrubbing.
+[See some examples of scrubbers here](https://github.com/flavorjones/loofah#loofahscrubber).
+
+Two new scrubbers have also been added: `PermitScrubber` and `TargetScrubber`.
+Read the [gem's readme](https://github.com/rails/rails-html-sanitizer) for more information.
+
+The documentation for `PermitScrubber` and `TargetScrubber` explains how you
+can gain complete control over when and how elements should be stripped.
+
 Upgrading from Rails 4.0 to Rails 4.1
 -------------------------------------