[css-syntax] Consolidate the definition of what the <urange> represents, so I can do error-checking in one spot.

Author: tabatkins

css-syntax/Overview.bs

@@ -2943,7 +2943,7 @@ The <<urange>> type</h3>
 	: <code>u '+' <<urange-codepoint>></code>
 	::
 		<a title="interpret a token as a hex integer">Interpret the &lt;urange-codepoint> as a hex integer</a>.
-		The <<urange>> represents a range consisting only of the resulting value.
+		Let <var>start value</var> and <var>end value</var> both be the returned value.
 
 	: <code>u '+' <<urange-codepoint>>? '?'+</code>
 	::
@@ -2952,25 +2952,33 @@ The <<urange>> type</h3>
 		otherwise, let <var>B</var> be zero.
 		Let <var>S</var> be the number of contiguous U+003F QUESTION MARK (?) codepoints.
 
-		The <<urange>> represents a contiguous range from
-		<code style="white-space: nowrap">B✕(16<sup>S</sup>)</code> to
-		<code style="white-space: nowrap">B✕(16<sup>S</sup>) + 16<sup>S+1</sup> − 1</code>,
-		inclusive.
+		Let <var>start value</var> be <code style="white-space: nowrap">B✕(16<sup>S</sup>)</code>.
+		Let <var>end value</var> be <code style="white-space: nowrap">B✕(16<sup>S</sup>) + 16<sup>S+1</sup> − 1</code>.
 
 	: <code>u '+' <<urange-codepoint>> <<negative-urange-codepoint>></code>
 	::
-		Let <var>starting value</var> be the result of <a title="interpret a token as a hex integer">interpreting the &lt;urange-codepoint> as a hex integer</a>.
-		Let <var>ending value</var> be the negation of the result of <a title="interpret a token as a hex integer">interpreting the &lt;negative-urange-codepoint> as a hex integer</a>.
+		Let <var>start value</var> be the result of <a title="interpret a token as a hex integer">interpreting the &lt;urange-codepoint> as a hex integer</a>.
+		Let <var>end value</var> be the negation of the result of <a title="interpret a token as a hex integer">interpreting the &lt;negative-urange-codepoint> as a hex integer</a>.
 
-		The <<urange>> represents a contiguous range from <var>starting value</var> to <var>ending value</var>, inclusive.
 
 	: <code>u '+' <<urange-range>></code>
 	::
 		Split the <<urange-range>>’s representation (or representation + unit)
 		into the two halves on either side of the U+002D HYPHEN-MINUS (-) codepoint.
 		Interpret each half as a hexadecimal integer.
 
-		The <<urange>> represents a contiguous range from the first half's value to the second half's value, inclusive.
+		Let <var>start value</var> be the first half's value.
+		Let <var>end value</var> be the second half's value.
+
+	To determine what codepoints the <<urange>> represents:
+
+	1. If <var>end value</var> is greater than the <a>maximum allowed code point</a>,
+		set it to the <a>maximum allowed code point</a>.
+
+	2. If <var>start value</var> is greater than <var>end value</var>,
+		the <<urange>> represents an empty range of codepoints.
+
+	3. Otherwise, the <<urange>> represents a contiguous range of codepoints from <var>start value</var> to <var>end value</var>, inclusive.
 
 	To <dfn>interpret a token as a hex integer</dfn>:
 

css-syntax/Overview.html

@@ -4405,7 +4405,7 @@ <h3 class="heading settled" data-level=7.1 id=urange-syntax><span class=secno>7.
 <dl><dt data-md=""><p><code>u '+' <a class="production css" data-link-type=type href=#typedef-urange-codepoint title="<urange-codepoint>">&lt;urange-codepoint&gt;</a></code></p>
 <dd data-md="">
 <p><a data-link-type=dfn href=#interpret-a-token-as-a-hex-integer title="interpret a token as a hex integer">Interpret the &lt;urange-codepoint&gt; as a hex integer</a>.
-The <a class="production css" data-link-type=type href=#typedef-urange title="<urange>">&lt;urange&gt;</a> represents a range consisting only of the resulting value.</p>
+Let <var>start value</var> and <var>end value</var> both be the returned value.</p>
 
 <dt data-md=""><p><code>u '+' <a class="production css" data-link-type=type href=#typedef-urange-codepoint title="<urange-codepoint>">&lt;urange-codepoint&gt;</a>? '?'+</code></p>
 <dd data-md="">
@@ -4414,26 +4414,34 @@ <h3 class="heading settled" data-level=7.1 id=urange-syntax><span class=secno>7.
 otherwise, let <var>B</var> be zero.
 Let <var>S</var> be the number of contiguous U+003F QUESTION MARK (?) codepoints.</p>
 
-<p>The <a class="production css" data-link-type=type href=#typedef-urange title="<urange>">&lt;urange&gt;</a> represents a contiguous range from
-<code style="white-space: nowrap">B✕(16<sup>S</sup>)</code> to
-<code style="white-space: nowrap">B✕(16<sup>S</sup>) + 16<sup>S+1</sup> − 1</code>,
-inclusive.</p>
+<p>Let <var>start value</var> be <code style="white-space: nowrap">B✕(16<sup>S</sup>)</code>.
+Let <var>end value</var> be <code style="white-space: nowrap">B✕(16<sup>S</sup>) + 16<sup>S+1</sup> − 1</code>.</p>
 
 <dt data-md=""><p><code>u '+' <a class="production css" data-link-type=type href=#typedef-urange-codepoint title="<urange-codepoint>">&lt;urange-codepoint&gt;</a> <a class="production css" data-link-type=type href=#typedef-negative-urange-codepoint title="<negative-urange-codepoint>">&lt;negative-urange-codepoint&gt;</a></code></p>
 <dd data-md="">
-<p>Let <var>starting value</var> be the result of <a data-link-type=dfn href=#interpret-a-token-as-a-hex-integer title="interpret a token as a hex integer">interpreting the &lt;urange-codepoint&gt; as a hex integer</a>.
-Let <var>ending value</var> be the negation of the result of <a data-link-type=dfn href=#interpret-a-token-as-a-hex-integer title="interpret a token as a hex integer">interpreting the &lt;negative-urange-codepoint&gt; as a hex integer</a>.</p>
+<p>Let <var>start value</var> be the result of <a data-link-type=dfn href=#interpret-a-token-as-a-hex-integer title="interpret a token as a hex integer">interpreting the &lt;urange-codepoint&gt; as a hex integer</a>.
+Let <var>end value</var> be the negation of the result of <a data-link-type=dfn href=#interpret-a-token-as-a-hex-integer title="interpret a token as a hex integer">interpreting the &lt;negative-urange-codepoint&gt; as a hex integer</a>.</p>
 
-<p>The <a class="production css" data-link-type=type href=#typedef-urange title="<urange>">&lt;urange&gt;</a> represents a contiguous range from <var>starting value</var> to <var>ending value</var>, inclusive.</p>
 
 <dt data-md=""><p><code>u '+' <a class="production css" data-link-type=type href=#typedef-urange-range title="<urange-range>">&lt;urange-range&gt;</a></code></p>
 <dd data-md="">
 <p>Split the <a class="production css" data-link-type=type href=#typedef-urange-range title="<urange-range>">&lt;urange-range&gt;</a>’s representation (or representation + unit)
 into the two halves on either side of the U+002D HYPHEN-MINUS (-) codepoint.
 Interpret each half as a hexadecimal integer.</p>
 
-<p>The <a class="production css" data-link-type=type href=#typedef-urange title="<urange>">&lt;urange&gt;</a> represents a contiguous range from the first half’s value to the second half’s value, inclusive.</p>
+<p>Let <var>start value</var> be the first half’s value.
+Let <var>end value</var> be the second half’s value.</p>
 </dl>
+<p>To determine what codepoints the <a class="production css" data-link-type=type href=#typedef-urange title="<urange>">&lt;urange&gt;</a> represents:</p>
+
+<ol><li data-md=""><p>If <var>end value</var> is greater than the <a data-link-type=dfn href=#maximum-allowed-code-point title="maximum allowed code point">maximum allowed code point</a>,
+set it to the <a data-link-type=dfn href=#maximum-allowed-code-point title="maximum allowed code point">maximum allowed code point</a>.</p>
+
+<li data-md=""><p>If <var>start value</var> is greater than <var>end value</var>,
+the <a class="production css" data-link-type=type href=#typedef-urange title="<urange>">&lt;urange&gt;</a> represents an empty range of codepoints.</p>
+
+<li data-md=""><p>Otherwise, the <a class="production css" data-link-type=type href=#typedef-urange title="<urange>">&lt;urange&gt;</a> represents a contiguous range of codepoints from <var>start value</var> to <var>end value</var>, inclusive.</p>
+</ol>
 <p>To <dfn data-dfn-type=dfn data-noexport="" id=interpret-a-token-as-a-hex-integer>interpret a token as a hex integer<a class=self-link href=#interpret-a-token-as-a-hex-integer></a></dfn>:</p>
 
 <ul><li data-md=""><p>If the token is a <a class="production css" data-link-type=type href=#typedef-number-token title="<number-token>">&lt;number-token&gt;</a> whose type flag is set to "integer",