Before adding form factor, the spec had two list-valued fields:

• Sec-CH-UA-Full-Version-List HTTP header / fullVersionList JS API
• Sec-CH-UA HTTP header / brands JS API

Introducing form factor creates a third list field, but it follows neither of the previous two precedents. Instead it uses the singular name "form factor".

Is this perhaps an oversight when working on #343, you forgot to consider renaming?