Define "user agent".

[jyasskin]

This definition draws from previous definitions in RFC 2616,
https://www.w3.org/TR/UAAG20/#def-user-agent,
https://www.w3.org/TR/CSS2/conform.html#user-agent, and
https://en.wikipedia.org/wiki/User_agent.

I am not at all tied to the particular wording of this definition or the choice of specification it appears in. If it moves to HTML, it can probably be more specific, maybe along the lines of https://www.w3.org/TR/CSS2/conform.html#user-agent.

Fixes whatwg/html#1021.

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Preview | Diff

[domenic]

Generally looks good. I'm a bit unsure about the "for example" connector, but probably it's the best way to go.

Let's leave this open for a bit more discussion, I suppose?

[GPHemsley]

Generally looks good. I'm a bit unsure about the "for example" connector, but probably it's the best way to go.

s/for example/such as/ ?

[annevk]

Merge this after TPAC when there's no more feedback?

[sideshowbarker]

Suggested change

	<p>A <dfn export>user agent</dfn> is any software that acts on behalf of a user, for example by
	<p>A <dfn export>user agent</dfn> is any software that acts on behalf of a user; for example by

[jyasskin]

The interwebs say to use a semicolon here (and a comma after) when the second bit is a complete sentence, which it isn't here. I don't feel strongly, of course.

[sideshowbarker]

The interwebs say to use a semicolon here (and a comma after) when the second bit is a complete sentence, which it isn't here. I don't feel strongly, of course.

I don’t feel strongly about it either — so it’s fine by me to leave it as-is

[GPHemsley]

I still think s/for example/such as/ is a better approach.

[annevk]

I kept it as "for example by" since "such as by" seemed awkward to me. Different approaches welcome though as follow-up PRs.