Editorial: fix language tag description (#1083)

index.html

@@ -557,18 +557,14 @@ <h3>
  such as fonts, styling, hyphenation, or text-to-speech voices for accessibility.
  </p>
  <p>
- A <dfn>language tag</dfn> is a <a>string</a> that matches the
- production of a `Language-Tag` defined in the [[BCP47]]
- specifications (see the <a href=
- "https://www.iana.org/assignments/language-subtag-registry">IANA
- Language Subtag Registry</a> for an authoritative list of possible
- values). That is, a language range is composed of one or more
- <dfn>subtags</dfn> that are delimited by a U+002D HYPHEN-MINUS ("-").
- For example, the '`en-AU`' language range represents English as
- spoken in Australia, and '`fr-CA`' represents French as spoken in
- Canada. Language tags that meet the validity criteria of [[RFC5646]]
- section 2.2.9 that can be verified without reference to the IANA
- Language Subtag Registry are considered structurally valid.
+ A <dfn>language tag</dfn> is a [=string=] that matches the production
+ of a well-formed `Language-Tag` defined in [[BCP47]].
+ </p>
+ <p class="note">
+ Language tags are case-insensitive. Examples of language tags include
+ '`fr`' (French), '`en-AU`' (English as spoken in Australia), or
+ '`zh-Hans-CN`' (Chinese as written in the Simplified Han script as
+ spoken in China).
  </p>
  <p>
  To <dfn>process the `lang` member</dfn>, given [=ordered map=]