Follow Google's HTML/CSS Style Guide. Exception: don't leave out optional elements.
In particular, here are a couple of basic guidelines from that style guide, which generally apply to other documentation source files, too (YAML, Markdown, etc.):
- Don't use tabs to indent text; use spaces only. Different text editors interpret tabs differently, and some Markdown features expect spaces and not tabs.
- Indent by 2 spaces per indentation level.
- Use all-lowercase for elements and attributes.
- Don't leave trailing spaces at the end of a line. (Except as needed for Markdown.)
Break lines at 80 characters except in the following cases:
- The metadata tags at the top of files (such as
page.metaDescription) have to be all on one line, so those lines can be as long as needed.
- If a URL in a link has a line break, the link won't work.
If a URL is longer than 80 characters (quite common), you're stuck with it. In that case,
put the URL on its own line with the
hrefattribute to make it easier to review the text before and after, as the following example shows:
You can find more information in <a href="https://example.com/long-url/johan-gambolputty-de-von-ausfern-…-von-hautkopf-of-ulm.html" class="external-link">his biography.</a>
Break code snippets (in <pre> blocks) at 80 characters.