Extensions docs

# Metadata

Extensions documents should follow the conventions outlined in the Add a Doc and Add a Blog Post guides. One notable exception is that we do not use the tags and author YAML front matter properties in extensions docs.

# Line wrapping

Extensions docs are wrapped at 100 characters. New content and updates to existing content must follow this convention save for the following exceptions:

• The existing page is already wrapped at another offset.
  • You may continue wrapping the document at the current offset.
• Rewrapping would introduce significant noise to a code review.
  • Limiting line wrapping normalization to the text blocks your PR touches.

# Header IDs

Header IDs are automatically generated based on the content of the header. This means that renaming a header will also change the header's ID and break existing links to that header.

To make your documentation more resilient to change, authors should manually declare header IDs.

### Common use cases {: #use-cases }

### Common use cases

Header IDs should be short and meaningful. Use descriptive names that unambiguously identify the content of the section rather than a kebab cased version of the header's text value.

# Link conventions

# Footer links

By convention, extensions docs strongly prefer named footer links over inline links. Named links have a couple of advantages over inline links.

• Named links are typically shorter. This makes it much easier to read and work with the source markdown file.
• Named links are easier to maintain. Authors can edit one link definition and update all uses of that link links across a given document.

Lorem ipsum dolor [sit amet][mdn-global], consectetur adipiscing elit.
Quisque aliquam rutrum pellentesque. Ut tincidunt purus ex, eget 
congue lacus aliquet quis.

[mdn-global]: https://developer.mozilla.org/en-US/docs/Glossary/Global_object

Lorem ipsum dolor [sit
amet](https://developer.mozilla.org/en-US/docs/Glossary/Global_object),
consectetur adipiscing elit. Quisque aliquam rutrum pellentesque. Ut
tincidunt purus ex, eget congue lacus aliquet quis.

# Internal links

When linking to other resources on developer.chrome.com, use the relative path from the site's root rather than a relative path from the page or a full URL.

[doc-page]: /docs/extensions/page/

[doc-page]: https://develper.chrome.com/docs/extensions/page/

[doc-page]: page/

Internal links should include a terminal slash.

[doc-page]: /docs/extensions/dir/page/
[doc-page]: /docs/extensions/sub/dir/page/#header

[doc-page]: /docs/extensions/dir/page
[doc-page]: /docs/extensions/sub/dir/page#header

# Code formatting

Code samples in extensions documentation should be formatted using the Chromium project's git cl format command. To use this command, you must first install depot_tools. See Using clang-format for additional details.

# Use this command to format JS files and code samples
git cl format --js <filename>

# Placeholder convention

Placeholders should be styled with <code><var>PLACEHOLDER_NAME</var></code> in body copy and PLACEHOLDER_NAME in code blocks and inline code. New content and updates to existing content must follow this convention.

chrome.runtime.sendMessage('EXTENSION_ID', MESSAGE, function() {
  if (chrome.runtime.lastError) {
    // Extension is not installed.
  }
}

chrome.runtime.sendMessage('<extension id>', <message>, function() {
  if (chrome.runtime.lastError) {
    // Extension is not installed.
  }
}