From WHATWG Wiki
- keepalive (though HTTP Keep-Alive [sic] header)
- referrer (though HTTP Referer [sic] header)
- whitespace (though CSS white-space [sic] property)
- newline (not line break)
- Use 's for possesives, even when it looks unnatural.
- Use the Oxford Comma.
- Avoid "one of" unless it's followed by a bulleted list. You can normally leave it out and just use "or". If you cannot leave it out, that might be a good indication you want to use a bulleted list for clarity.
- web, unless at the start of a sentence
- Spaces around — (em dash)
- Lowercase after colon (The slot attribute is used to assign a slot to an element: an element with a slot attribute is assigned to the slot created by the slot element whose name attribute's value matches that slot attribute's value)
- Avoid using "simply" or suggesting that something is simple