Add Action Text to guides [ci skip]

- Move some actiontext/README.md content to Action Text Overview guide
- I added WIP label to that guide since we definitely want to complement it.
- Add Action Text to Major Features of Rails 6.0

Similar approach was used in #34812

1 files changed, 99 insertions, 0 deletions

diff --git a/guides/source/action_text_overview.md b/guides/source/action_text_overview.md
new file mode 100644
index 0000000000..08ec35e52a
--- /dev/null
+++ b/guides/source/action_text_overview.md
@@ -0,0 +1,99 @@
+**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.**
+
+Action Text Overview
+====================
+
+This guide provides you with all you need to get started in handling
+rich text content.
+
+After reading this guide, you will know:
+
+* How to configure Action Text.
+* How to handle rich text content.
+* How to style rich text content.
+
+--------------------------------------------------------------------------------
+
+Introduction
+------------
+
+Action Text brings rich text content and editing to Rails. It includes
+the [Trix editor](https://trix-editor.org) that handles everything from formatting
+to links to quotes to lists to embedded images and galleries.
+The rich text content generated by the Trix editor is saved in its own
+RichText model that's associated with any existing Active Record model in the application.
+Any embedded images (or other attachments) are automatically stored using
+Active Storage and associated with the included RichText model.
+
+## Trix compared to other rich text editors
+
+Most WYSIWYG editors are wrappers around HTML’s `contenteditable` and `execCommand` APIs,
+designed by Microsoft to support live editing of web pages in Internet Explorer 5.5,
+and [eventually reverse-engineered](https://blog.whatwg.org/the-road-to-html-5-contenteditable#history)
+and copied by other browsers.
+
+Because these APIs were never fully specified or documented,
+and because WYSIWYG HTML editors are enormous in scope, each
+browser's implementation has its own set of bugs and quirks,
+and JavaScript developers are left to resolve the inconsistencies.
+
+Trix sidesteps these inconsistencies by treating contenteditable
+as an I/O device: when input makes its way to the editor, Trix converts that input
+into an editing operation on its internal document model, then re-renders
+that document back into the editor. This gives Trix complete control over what
+happens after every keystroke, and avoids the need to use execCommand at all.
+
+## Installation
+
+Run `rails action_text:install` to add the Yarn package and copy over the necessary migration.
+
+## Examples
+
+Adding a rich text field to an existing model:
+
+```ruby
+# app/models/message.rb
+class Message < ApplicationRecord
+  has_rich_text :content
+end
+```
+
+Then refer to this field in the form for the model:
+
+```erb
+<%# app/views/messages/_form.html.erb %>
+<%= form_with(model: message) do |form| %>
+  <div class="field">
+    <%= form.label :content %>
+    <%= form.rich_text_area :content %>
+  </div>
+<% end %>
+```
+
+And finally display the sanitized rich text on a page:
+
+```erb
+<%= @message.content %>
+```
+
+To accept the rich text content, all you have to do is permit the referenced attribute:
+
+```ruby
+class MessagesController < ApplicationController
+  def create
+    message = Message.create! params.require(:message).permit(:title, :content)
+    redirect_to message
+  end
+end
+```
+
+## Custom styling
+
+By default, the Action Text editor and content is styled by the Trix defaults.
+If you want to change these defaults, you'll want to remove
+the `app/assets/stylesheets/actiontext.css` linker and base your stylings on
+the [contents of that file](https://raw.githubusercontent.com/basecamp/trix/master/dist/trix.css).
+
+You can also style the HTML used for embedded images and other attachments (known as blobs).
+On installation, Action Text will copy over a partial to
+`app/views/active_storage/blobs/_blob.html.erb`, which you can specialize.