Merge branch 'docs-video-style' into 'master'

Docs: Update style guide for videos

See merge request gitlab-org/gitlab-ce!29683

doc/development/documentation/styleguide.md

@@ -100,6 +100,13 @@ use regular Markdown markup, following the rules in the linked style guide.
 
 Note that Kramdown-specific markup (e.g., `{:.class}`) will not render properly on GitLab instances under [`/help`](index.md#gitlab-help).
 
+Hard-coded HTML is valid, although it's discouraged to be used while we have `/help`. HTML is permitted as long as:
+
+- There's no equivalent markup in markdown.
+- Advanced tables are necessary.
+- Special styling is required.
+- Reviewed and approved by a technical writer.
+
 ## Structure
 
 ### Organize by topic, not by type
@@ -143,7 +150,8 @@ The table below shows what kind of documentation goes where.
    a proper naming would be `import_projects_from_github.md`. The same rule
    applies to images.
 1. For image files, do not exceed 100KB.
-1. We do not yet support embedded videos. Please link out.
+1. Do not upload video files to the product repositories.
+[Link or embed videos](#videos) instead.
 1. There are four main directories, `user`, `administration`, `api` and `development`.
 1. The `doc/user/` directory has five main subdirectories: `project/`, `group/`,
    `profile/`, `dashboard/` and `admin_area/`.
@@ -207,6 +215,7 @@ Do not include the same information in multiple places. [Link to a SSOT instead.
 
 ## Text
 
+- [Write in markdown](#markdown).
 - Splitting long lines (preferably up to 100 characters) can make it easier to provide feedback on small chunks of text.
 - Insert an empty line for new paragraphs.
 - Use sentence case for titles, headings, labels, menu items, and buttons.
@@ -430,7 +439,7 @@ To indicate the steps of navigation through the UI:
 - Images should be used (only when necessary) to _illustrate_ the description
   of a process, not to _replace_ it.
 - Max image size: 100KB (gifs included).
-- The GitLab docs do not support videos yet.
+- See also how to link and embed [videos](#videos) to illustrate the docs.
 
 Inside the document:
 
@@ -455,6 +464,85 @@ directly to an HTML `img` tag:
 <img src="path/to/image.jpg" alt="Alt text (required)" class="image-noshadow">
 ```
 
+## Videos
+
+Adding GitLab's existing YouTube video tutorials to the documentation is
+highly encouraged, unless the video is outdated. Videos should not
+replace documentation, but complement or illustrate it. If content in a video is
+fundamental to a feature and its key use cases, but this is not adequately covered in the documentation,
+add this detail to the documentation text or create an issue to review the video and do so.
+
+Do not upload videos to the product repositories. [Link](#link-to-video) or [embed](#embed-videos) them instead.
+
+### Link to video
+
+To link out to a video, include a YouTube icon so that readers can 
+quickly and easily scan the page for videos before reading:
+
+```md
+<i class="fa fa-youtube-play youtube" aria-hidden="true"></i>
+For an overview, see [Video Title](link-to-video).
+```
+
+You can link any up-to-date video that is useful to the GitLab user.
+
+### Embed videos
+
+> [Introduced](https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/472) in GitLab 12.1.
+
+GitLab docs (docs.gitlab.com) support embedded videos.
+
+You can only embed videos from
+[GitLab's official YouTube account](https://www.youtube.com/channel/UCnMGQ8QHMAnVIsI3xJrihhg).
+For videos from other sources, [link](#link-to-video) them instead.
+
+In most cases, it is better to [link to video](#link-to-video) instead,
+because an embed takes up a lot of space on the page and can be distracting
+to readers.
+
+To embed a video, follow the instructions below and make sure
+you have your MR reviewed and approved by a technical writer.
+
+1. Copy the code below and paste it into your markdown file.
+  Leave a blank line above and below it. Do NOT edit the code
+  (don't remove or add any spaces, etc).
+1. On YouTube, visit the video URL you want to display. Copy
+  the regular URL from your browser (`https://www.youtube.com/watch?v=VIDEO-ID`)
+  and replace the video title and link in the line under `<div class="video-fallback">`.
+1. On YouTube, click **Share**, then **Embed**.
+1. Copy the `<iframe>` source (`src`) **URL only**
+  (`https://www.youtube.com/embed/VIDEO-ID`),
+  and paste it, replacing the content of the `src` field in the
+  `iframe` tag.
+
+```html
+leave a blank line here
+<div class="video-fallback">
+  See the video: [Video title](https://www.youtube.com/watch?v=MqL6BMOySIQ).
+</div>
+<figure class="video-container">
+  <iframe src="https://www.youtube.com/embed/MqL6BMOySIQ" frameborder="0" allowfullscreen="true"> </iframe>
+</figure>
+leave a blank line here
+```
+
+This is how it renders on docs.gitlab.com:
+
+<div class="video-fallback">
+  See the video: [What is GitLab](https://www.youtube.com/watch?v=enMumwvLAug).
+</div>
+<figure class="video-container">
+  <iframe src="https://www.youtube.com/embed/MqL6BMOySIQ" frameborder="0" allowfullscreen="true"> </iframe>
+</figure>
+
+> Notes:
+>
+> - The `figure` tag is required for semantic SEO and the `video_container`
+class is necessary to make sure the video is responsive and displays
+nicely on different mobile devices.
+> - The `<div class="video-fallback">` is a fallback necessary for GitLab's
+`/help`, as GitLab's markdown processor does not support iframes. It's hidden on the docs site but will be displayed on GitLab's `/help`.
+
 ## Code blocks
 
 - Always wrap code added to a sentence in inline code blocks (``` ` ```).