Do not allow duplicate variants within the tlang component of a trans…

…formed content extension.

spec/locales-currencies-tz.html

@@ -40,17 +40,33 @@ <h1>Unicode Locale Extension Sequences</h1>
       <h1>IsStructurallyValidLanguageTag ( _locale_ )</h1>
 
       <p>
-        The IsStructurallyValidLanguageTag abstract operation verifies that the _locale_ argument (which must be a String value)
+        The IsStructurallyValidLanguageTag abstract operation verifies that the _locale_ argument (which must be a String value) represents a well-formed "Unicode BCP 47 locale identifier", consistent with <a href="https://unicode.org/reports/tr35/#Unicode_locale_identifier">Unicode Technical Standard 35 section 3.2</a>.
+      </p>
+
+      <p>
+        IsStructurallyValidLanguageTag returns *true* if all of the following conditions hold, *false* otherwise:
       </p>
 
       <ul>
-        <li>represents a well-formed "Unicode BCP 47 locale identifier" as specified in <a href="https://unicode.org/reports/tr35/#Unicode_locale_identifier">Unicode Technical Standard 35 section 3.2</a>,</li>
-        <li>does not include duplicate variant subtags, and</li>
-        <li>does not include duplicate singleton subtags.</li>
+        <li>_locale_ can be generated from the EBNF grammar in section 3.2 of the Unicode Technical Standard 35, starting with `unicode_locale_id`;</li>
+        <li>_locale_ does not use any of the backwards compatiblity syntax described in <a href="https://unicode.org/reports/tr35/#BCP_47_Conformance">Unicode Technical Standard #35 LDML § 3.3 BCP 47 Conformance</a>; and</li>
+        <li>interpreting _locale_ as `unicode_locale_id`,
+          <ul>
+            <li>the `unicode_language_id` within _locale_ does not contain ASCII case-insensitively equivalent `unicode_variant_subtag` subtags, and</li>
+            <li>if _locale_ contains an `extensions*` component, that component
+              <ul>
+                <li>contains at most one `unicode_locale_extensions` component,</li>
+                <li>contains at most one `transformed_extensions` component,</li>
+                <li>does not contain multiple `other_extensions` components with ASCII case-insensitively equivalent `[alphanum-[tTuUxX]]` subtags, and</li>
+                <li>if a `transformed_extensions` component is present and contains a `tlang` component, then the `(sep unicode_variant_subtag)*` within the `tlang` component does not contain ASCII case-insensitively equivalent `unicode_variant_subtag` subtags.
+              </ul>
+            </li>
+          </ul>
+        </li>
       </ul>
 
       <p>
-        The abstract operation returns true if _locale_ can be generated from the EBNF grammar in section 3.2 of the Unicode Technical Standard 35, starting with `unicode_locale_id`, and does not contain duplicate variant or singleton subtags (other than as a private use subtag). It returns false otherwise. Terminal value characters in the grammar are interpreted as the Unicode equivalents of the ASCII octet values given.
+        When evaluating each condition, terminal value characters in the grammar are interpreted as the corresponding ASCII code points.
       </p>
     </emu-clause>