[css-value-3] Define new bracketed range notation for the CSS value definition syntax. #355

Author: fantasai

css-values-3/Overview.bs

@@ -76,8 +76,10 @@ Module Interactions</h3>
 <h2 id="value-defs">
 Value Definition Syntax</h2>
 
-	The syntax described here is used to define the set of valid values
-	for CSS properties. A property value can have one or more components.
+	The <dfn for=CSS export>value definition syntax</dfn> described here
+	is used to define the set of valid values for CSS properties
+	(and the valid syntax of many other parts of CSS).
+	A value so described can have one or more components.
 
 <h3 id="component-types">
 Component value types</h3>
@@ -92,6 +94,9 @@ Component value types</h3>
 		<li>
 			basic data types, which appear between ''&lt;'' and ''>''
 			(e.g., <<length>>, <<percentage>>, etc.).
+			For <a>numeric data types</a>,
+			this type notation can annotate any range restrictions
+			using the [[#numeric-ranges|bracketed range notation]] described below.
 
 		<li>
 			types that have the same range of values as a property bearing the same name
@@ -355,7 +360,11 @@ Property value examples</h3>
 <h2 id="textual-values">
 Textual Data Types</h2>
 
-	<dfn export lt="CSS identifier | CSS ident | identifier | ident">Identifiers</dfn>,
+	The <dfn>textual data types</dfn> include
+	various keywords and identifiers
+	as well as strings (<<string>>) and URLs (<<url>>).
+
+	CSS <dfn export lt="CSS identifier | CSS ident | identifier | ident">identifiers</dfn>,
 	generically denoted by <dfn>&lt;ident></dfn>,
 	consist of a sequence of characters conforming to the <<ident-token>> grammar. [[!CSS3SYN]]
 	Identifiers cannot be quoted;
@@ -665,14 +674,52 @@ URL Modifiers</h4>
 <h2 id="numeric-types">
 Numeric Data Types</h2>
 
-	Properties may restrict numeric values to some range.
+	The <dfn>numeric data types</dfn> include
+	<<integer>>,
+	<<number>>,
+	<<percentage>>,
+	and various <a>dimensions</a>
+	including <<length>>, <<angle>>, <<time>>, <<frequency>>, and <<resolution>>.
+
+	Note: While genera-purpose <a>dimensions</a> are defined here,
+	some other modules define additional data types
+	(e.g. [[css-grid-1]] introduces ''fr'' units)
+	whose usage is more localized.
+
+<h2 id="numeric-ranges">
+Range Restrictions and Range Definition Notation</h3>
+
+	Properties can restrict numeric values to some range.
 	If the value is outside the allowed range,
-	unless otherwise specified,
+	then unless otherwise specified,
 	the declaration is invalid and must be <a href="https://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
+	Range restrictions can be annotated in the numeric type notation
+	using <dfn>bracketed range notation</dfn>,
+	<code>[<var>min</var>,<var>max</var>]</code>
+	within the angle brackets, after the identifying keyword,
+	indicating a closed range
+	between (and including) <var>min</var> and <var>max</var>,
+	e.g. <<integer [0,10]>>.
+
+	Note: CSS values generally do not allow open ranges;
+	thus only square-bracket notation is used.
 
 	CSS theoretically supports infinite precision and infinite ranges for all value types;
 	however in reality implementations have finite capacity.
 	UAs should support reasonably useful ranges and precisions.
+	Range extremes that are ideally unlimited
+	are indicated using &infin; or &minus;&infin; as appropriate.
+
+	If no range is indicated,
+	either by using the <a>bracketed range notation</a>
+	or in the property description,
+	then <code>[&minus;&infin;,&infin;]</code> is assumed.
+
+	Note: At the time of writing,
+	the <a>bracketed range notation</a> is new;
+	thus in most CSS specifications
+	any range limitations are described only in prose.
+	This does not make them any less binding.
 <!--
 	The recommended minimum ranges and precision,
 	and the required rounding and clamping rules,