[css-values] Rewrite url() to recognize that it's now an ordinary function most of the time.

--HG--
extra : rebase_source : 5947bcdd4521625135d45a25619ec5f743823ca2

Author: tabatkins

css-values/Overview.bs

@@ -138,7 +138,7 @@ Component value types</h3>
 		If commas were not implicitly omittable,
 		the grammar would have to be much more complicated
 		to properly express the ways that the arguments can be omitted,
-		greatly obscuring the simplicity of the feature.
+		greatly obscURLng the simplicity of the feature.
 	</div>
 
 	All CSS properties also accept the <a href="#common-keywords">CSS-wide keyword values</a>
@@ -450,49 +450,60 @@ Quoted Strings: the <<string>> type</h3>
 Resource Locators: the <<url>> type</h3>
 
 	A <dfn>URL</dfn> is a pointer to a resource
-	and is a <a title="consume a url token" spec=css-syntax>specially-parsed</a> <a href="#functional-notation">functional notation</a>
-	denoted by <dfn id="url-value">&lt;url></dfn>.
-	It corresponds to the <<url-token>> production
-	in the <a href="http://www.w3.org/TR/css-syntax/">CSS Syntax Module</a> [[!CSS3SYN]].
+	and is a <a href="#functional-notation">functional notation</a>
+	denoted by <<url>>.
+	The syntax of a <<url>> is:
+
+	<pre class="prod"><dfn id="url-value">&lt;url></dfn> = url( <<string>> <<url-modifier>>* )</pre>
+
 
 	<div class="example">
 		Below is an example of a URL being used as a background image:
 
 		<pre>body { background: url("http://www.example.com/pinkish.gif") }</pre>
+	</div>
 
-		The same example can be written without quotes:
+	In addition to the syntax defined above,
+	a <<url>> can sometimes be written in other ways:
 
-		<pre>body { background: url(http://www.example.com/pinkish.gif) }</pre>
-	</div>
+	* For legacy reasons,
+		a <<url>> can be written without quotation marks around the URL itself.
+		This syntax is <a title="consume a url token" spec=css-syntax>specially-parsed</a>,
+		and produces a <<url-token>> rather than a <a>function</a> syntactically. [[!CSS3SYN]]
+	* Some CSS contexts, such as ''@import'', allow a <<url>> to be represented by a <<string>> instead.
+		This behaves identically to writing a ''url()'' function containing that string.
 
-	Note: Note that in some CSS syntactic contexts (as defined by that context),
-	a URL can be represented as a <<string>> rather than by <<url>>.
-	An example of this is the ''@import'' rule.
+	Because these alternate ways of writing a <<url>> are not <a>functional notations</a>,
+	they cannot accept any <<url-modifier>>s.
 
-	Parentheses, whitespace characters, single quotes (&#39;) and double quotes (") appearing in a URL
-	must be escaped with a backslash
-	so that the resulting value is a valid <<url-token>>,
+	Note: The special parsing rules for the legacy quotation mark-less <<url>> syntax
+	means that parentheses, whitespace characters, single quotes (&#39;) and double quotes (") appearing in a URL
+	must be escaped with a backslash,
 	e.g. ''url(open\(parens)'', ''url(close\)parens)''.
 	Depending on the type of URL,
-	it might also be possible to write these characters as URI-escapes
+	it might also be possible to write these characters as URL-escapes
 	(e.g. ''url(open%28parens)'' or ''url(close%29parens)'')
-	as described in [[URI]].
-	Alternatively a URL containing such characters may be represented as a quoted <a>string</a> within the ''url()'' notation.
+	as described in [[URL]].
+	(If written as a normal function containing a string, ordinary string escaping rules apply;
+		only newlines and the character used to quote the string need to be escaped.)
+
+<h4 id="relative-urls">
+Relative URLs</h4>
 
 	In order to create modular style sheets that are not dependent on
-	the absolute location of a resource, authors should use relative URIs.
-	Relative URIs (as defined in [[!URI]]) are resolved to full URIs
-	using a base URI. RFC&nbsp;3986, section&nbsp;3, defines the normative
+	the absolute location of a resource, authors should use relative URLs.
+	Relative URLs (as defined in [[!URL]]) are resolved to full URLs
+	using a base URL. RFC&nbsp;3986, section&nbsp;3, defines the normative
 	algorithm for this process.
-	For CSS style sheets, the base URI is that of the style sheet itself,
+	For CSS style sheets, the base URL is that of the style sheet itself,
 	not that of the styled source document.
 	Style sheets embedded within a document have
 	the base URL associated with their container.
 
 	When a <<url>> appears in the computed value of a property,
 	it is resolved to an absolute URL,
 	as described in the preceding paragraph.
-	The computed value of a URI that the UA cannot resolve to an absolute URI is the specified value.
+	The computed value of a URL that the UA cannot resolve to an absolute URL is the specified value.
 
 	<div class="example">
 		For example, suppose the following rule:
@@ -511,6 +522,17 @@ Resource Locators: the <<url>> type</h3>
 		The same image will be used regardless of the URL of the source document containing the <code>&lt;body></code>.
 	</div>
 
+<h4 id='url-modifiers'>
+URL Modifiers</h4>
+
+	The ''url()'' function supports specifying additional <dfn>&lt;url-modifier></dfn>s,
+	which change the meaning or the interpretation of the URL somehow.
+	A <<url-modifier>> is either an <<ident>> or a <a>function</a>.
+
+	This specification does not define any <<url-modifier>>s,
+	but other specs may do so.
+
+
 <h2 id="numeric-types">
 Numeric Data Types</h2>
 
@@ -681,7 +703,7 @@ Font-relative lengths: the ''em'', ''ex'', ''ch'', ''rem'' units</h4>
 			The x-height of a font can be found in different ways. Some fonts
 			contain reliable metrics for the x-height. If reliable font metrics
 			are not available, UAs may determine the x-height from the height
-			of a lowercase glyph. One possible heuristic is to look at how far
+			of a lowercase glyph. One possible heURLstic is to look at how far
 			the glyph for the lowercase "o" extends below the baseline, and
 			subtract that value from the top of its bounding box. In the cases
 			where it is impossible or impractical to determine the x-height,
@@ -993,22 +1015,22 @@ Images: the <<image>> type</h3>
 <h2 id="functional-notation">
 Functional Notations</h2>
 
-		A <dfn>functional notation</dfn> is a type of component value
-		that can represent more complex types or invoke special processing.
-		The syntax starts with the name of the function
-		immediately followed by a left parenthesis
-		(i.e. a <<function-token>>)
-		followed by the argument(s) to the notation
-		followed by a right parenthesis.
-		White space is allowed, but optional, immediately inside the parentheses.
-		Functions can take multiple arguments,
-		which are formatted similarly to a CSS property value.
-
-		Some legacy functional notations, such as ''rgba()'', use commas unnecessarily,
-		but generally commas are only used to separate items in a list,
-		or pieces of a grammar that would be ambiguous otherwise.
-		If a comma is used to separate arguments,
-		whitespace is optional before and after the comma.
+	A <dfn>functional notation</dfn> is a type of component value
+	that can represent more complex types or invoke special processing.
+	The syntax starts with the name of the function
+	immediately followed by a left parenthesis
+	(i.e. a <<function-token>>)
+	followed by the argument(s) to the notation
+	followed by a right parenthesis.
+	White space is allowed, but optional, immediately inside the parentheses.
+	Functions can take multiple arguments,
+	which are formatted similarly to a CSS property value.
+
+	Some legacy functional notations, such as ''rgba()'', use commas unnecessarily,
+	but generally commas are only used to separate items in a list,
+	or pieces of a grammar that would be ambiguous otherwise.
+	If a comma is used to separate arguments,
+	whitespace is optional before and after the comma.
 
 	<div class="example">
 		<pre>
@@ -1059,7 +1081,7 @@ Mathematical Expressions: ''calc()''</h3>
 
 	<div class="example">
 		The following sets the 'font-size' so that exactly 40em fits within the viewport,
-		ensuring that roughly the same amount of text always fills the screen no matter the screen size.
+		ensURLng that roughly the same amount of text always fills the screen no matter the screen size.
 
 		<pre>
 		:root {
@@ -1482,7 +1504,7 @@ Ian's proposal:
 		<dd>
 			The attribute value is taken as the contents of a CSS <<string>>.
 			It is interpreted as a quoted string within the ''url()'' notation.
-			The default is ''about:invalid'', which is a URI defined (<a href="#about-invalid">in Appendix A</a>) to point
+			The default is ''about:invalid'', which is a URL defined (<a href="#about-invalid">in Appendix A</a>) to point
 			to a non-existent document with a generic error condition.
 			Relative URLs must be made absolute
 			according to the rules of the document language as applied to URLs originating from the element;
@@ -1698,11 +1720,11 @@ Appendix A: IANA Considerations</h2>
 <h3 id='about-invalid'>
 Registration for the <code>about:invalid</code> URL scheme</h3>
 
-	This sections defines and registers the <code>about:invalid</code> URI,
+	This sections defines and registers the <code>about:invalid</code> URL,
 	in accordance with the registration procedure defined in [[RFC6694]].
 
 
-	The official record of this registration can be found at <a href="http://www.iana.org/assignments/about-uri-tokens/about-uri-tokens.xml">http://www.iana.org/assignments/about-uri-tokens/about-uri-tokens.xml</a>.
+	The official record of this registration can be found at <a href="http://www.iana.org/assignments/about-URL-tokens/about-URL-tokens.xml">http://www.iana.org/assignments/about-URL-tokens/about-URL-tokens.xml</a>.
 
 	<table class="data define">
 		<tr>
@@ -1711,8 +1733,8 @@ Registration for the <code>about:invalid</code> URL scheme</h3>
 		<tr>
 			<th>Intended Usage
 			<td>
-				The <code>about:invalid</code> URI references a non-existent document with a generic error condition.
-				It can be used when a URI is necessary, but the default value shouldn't be resolveable as any type of document.
+				The <code>about:invalid</code> URL references a non-existent document with a generic error condition.
+				It can be used when a URL is necessary, but the default value shouldn't be resolveable as any type of document.
 		<tr>
 			<th>Contact/Change controller
 			<td>CSS WG &lt;<a href="mailto:www-style@w3.org">www-style@w3.org</a>> (on behalf of W3C)