[css2] Minor fixes + fixes to charset section based on mail thread

ianbjacobs · ianbjacobs · commit 4ed62165d983 · 1998-02-10T22:28:42.000Z
--HG--
extra : convert_revision : svn%3A73dc7c4b-06e6-40f3-b4f7-9ed1dbc14bfc/trunk%40857
diff --git a/css2/syndata.src b/css2/syndata.src
@@ -1,6 +1,6 @@
 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
 <html lang="en">
-<!-- $Id: syndata.src,v 2.1 1998-02-10 00:16:10 ijacobs Exp $ -->
+<!-- $Id: syndata.src,v 2.2 1998-02-10 22:28:42 ijacobs Exp $ -->
 <HEAD>
 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
 <TITLE>CSS2 syntax and basic data types</TITLE>
@@ -149,12 +149,15 @@ href="#escaped-characters">escaped characters.</a>
     <LI> <a name="escaped-characters">The backslash</a> (\) followed
     by at most six hexadecimal digits (0..9A..F) stands for the <a
     rel="biblioentry" href="./refs.html#ref-ISO10646">[ISO10646]</a>
-    character with that number. 
+    character with that number. The first space following the
+    hexadecimal sequence is ignored. This allows authors to avoid
+    ambiguities between, for example, hexadecimal "\26C" and
+    hexadecimal "\26" followed immediately by the letter "C".
 
     <LI> Any character except a hexadecimal digit can be escaped to
     remove its special meaning, by putting a backslash (\) in front,
     For example, <samp>"\""</samp> is a string consisting of one
-    double quote.
+    double quote. 
 
     <LI> The two preceding items define <span class="index-inst"
     title="backslash
@@ -542,14 +545,16 @@ display to a laser printer).
 </PRE>
 </div>
 
-<P>The 'em' unit, as used in CSS, is equal to the <span
-class="index-inst" title="font size">font size</span> used when
-rendering an element's text. It may be used for vertical or horizontal
-measurement. The 'ex' unit is equal to the font's <span
-class="index-def" title="x-height"><dfn>x-height</dfn></span> (the
-height of the letter 'x') of the element's font. A font need not
-contain the letter "M" to have an 'em' size or the letter "x" to have
-an x-height; the font should still define the two units.
+<P>The 'em' unit refers to the <span class="index-def"
+title="em-height"><a name="em-height"><dfn>em-height</dfn></a></span>.
+In CSS, the em-height is equal to the <span class="index-inst"
+title="font size">font size</span> used when rendering an element's
+text. It may be used for vertical or horizontal measurement. The 'ex'
+unit is equal to the font's <span class="index-def"
+title="x-height"><dfn>x-height</dfn></span> (the height of the letter
+'x') of the element's font. A font need not contain the letter "M" to
+have an 'em' size or the letter "x" to have an x-height; the font
+should still define the two units.
 
 <!-- Incomplete -->
 
@@ -602,7 +607,7 @@ href="cascade.html#computed-value">computed values</a>.  For example:</p>
 <PRE>
   BODY {
     font-size: 12pt;
-    text-indent: 3em;  /* i.e. 36pt */
+    text-indent: 3em;  /* i.e., 36pt */
   }
   H1 { font-size: 15pt } 
 </PRE>
@@ -643,9 +648,12 @@ is an optional sign character ('+' or '-', with '+' being the default)
 immediately followed by a number immediately followed by '%'.
 
 <P> Percentage values are always relative to another value, for
-example a length. Each property that allows percentages also
-defines to which value the percentage refers. When a percentage value
-is set for a property of the root of the <a
+example a length. Each property that allows percentages also defines
+the value to which the percentage refers. The value may be that of
+another property for the same element, a property for an ancestor
+element, or a value of the rendering context (e.g., the width of a <a
+href="visuren.html#containing-block">containing block</a>). When a
+percentage value is set for a property of the root of the <a
 href="conform.html#doctree">document tree</a> and the percentage is
 defined as referring to the inherited value of some property X, the
 resultant value is the percentage times the <a
@@ -660,7 +668,7 @@ the percentage value (120%):
 
 <PRE>
   P { font-size: 10pt }
-  P { line-height: 120% }  /* relative to 'font-size', i.e. 12pt */
+  P { line-height: 120% }  /* relative to 'font-size', i.e., 12pt */
 </PRE>
 </div>
 
@@ -824,7 +832,7 @@ identifier is optional.
 <P>These following are legal angle unit identifiers:</p>
 
 <ul>
-<li><strong>deg</strong>: degrees.
+<li><strong>deg</strong>: degrees
 <LI><strong>grad</strong>: gradient
 <LI><strong>rad</strong>: radians
 </UL>
@@ -926,28 +934,26 @@ A[TITLE="a not so very long title"] {border: double}
 
 <P>A CSS style sheet is a sequence of characters from the Universal
 Character Set, defined in <a rel="biblioentry"
-href="./refs.html#ref-ISO10646">[ISO10646]</a> (see <a
-rel="biblioentry" href="./refs.html#ref-HTML40"
-class="informref">[HTML40]</a>, Chapter 5, for a discussion of
-character sets and character encodings).  For transmission and
+href="./refs.html#ref-ISO10646">[ISO10646]</a>. For transmission and
 storage, these characters must be <span class="index-def"
 title="character encoding">encoded</span> by a character encoding that
-supports the ASCII character set and in which the ASCII characters
-are encoded as themselves (e.g., ISO 8859-1, SHIFT JIS, etc.).
-
-<!-- Bert doesn't agree. What about EBCDIC? -IJ -->
+supports the ASCII character set (e.g., ISO 8859-x, SHIFT JIS, etc.).
+For a good introduction to character sets and character encodings,
+please consult <a rel="biblioentry" href="./refs.html#ref-HTML40"
+class="informref">[HTML40]</a>, Chapter 5.
 
 <P>When a style sheet is embedded in another document, the style sheet
-shares the character encoding of the whole document (which is
-determined by the <a href="conform.html#doclanguage">document
-language</a>). In HTML, for example, the character encoding may be
-specified by HTTP headers or the META element, as in:
+shares the character encoding of the whole document. ("Embedded" here
+means textual inclusion, not embedded byte sequences.)  For
+example, in <a rel="biblioentry" href="./refs.html#ref-HTML40"
+class="informref">[HTML40]</a>, the "charset" attribute of many
+elements (META, LINK, A, etc.) designates the character encoding, as
+in:</p>
 
 <pre>
 &lt;META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"&gt;
 </pre>
 
-
 <P>When a style sheet resides in a separate file, user agents must
 observe the following <span class="index-inst" title="character
 encoding::user agent's determination of">priorities</span> when
@@ -957,25 +963,22 @@ encoding</span> (from highest priority to lowest):</p>
 
 <ol>
 <li>An HTTP "charset" parameter in a "Content-Type" field.
+<li>The <span class="index-def" title="@charset">@charset</span>
+at-rule. 
 <li>Mechanisms of the language of the
 referencing document (e.g., in HTML, the "charset" 
 attribute of the LINK element). 
-<li>The <span class="index-def" title="@charset">@charset</span>
-at-rule. 
 </ol>
 
-<!-- This same "general-to-specific" ordering in HTML 4.0 has raised
-some eyebrows, but recently received support from the HTML WG
-in the html-editors mailing list -IJ -->
-
 <P>When present, only one @charset rule may appear in an external
 style sheet -- it must <em>not</em> appear in an embedded style sheet
--- and it must be the first data in the document. After "@charset",
-authors specify the name of a character encoding. The name must be a
-charset name as described in <a href="refs.html#ref-IANA"
-class="normref">[IANA]</a> registry (see <a rel="biblioentry"
-href="./refs.html#ref-CHARSETS" class="informref">[CHARSETS]</a>
-for a complete list). For example:</p>
+-- and it must be the first line in the document (not preceded by any
+other characters). After "@charset", authors specify the name of a
+character encoding. The name must be a charset name as described in <a
+href="refs.html#ref-IANA" class="normref">[IANA]</a> registry (see <a
+rel="biblioentry" href="./refs.html#ref-CHARSETS"
+class="informref">[CHARSETS]</a> for a complete list). For
+example:</p>
 
 <div class="example"><P>
 @charset "ISO-8859-1";
@@ -984,40 +987,71 @@ for a complete list). For example:</p>
 <P>This specification does not mandate which character encodings
 a user agent must support.
 
+<P>What purpose does the @charset construct serve if user agents
+cannot understand it before they know the character encoding?  It acts
+as a verification mechanism. In the case HTTP headers do not provide
+character encoding information, user agents may attempt to guess the
+character set, and should they succeed, the @charset allows them to
+double check their guess. For this reason, character encodings in
+which the ASCII characters are encoded as themselves are more likely
+to help user agents determine the correct character encoding than
+other encodings schemes.
+
 <!-- More examples of good encodings to use? -IJ -->
 
 <!-- Encodings not to use? (cf. HTML 4.0) -IJ -->
 
-<h3>Encoding characters not represented in a character encoding</h3>
+<h3>Referring to characters not represented in a character encoding</h3>
 
 <P>A style sheet may have to refer to characters that cannot be
 represented in the current character encoding.  These characters must
 be written as <a href="#escaped-characters">escaped</a> references to
 <a rel="biblioentry" href="./refs.html#ref-ISO10646">[ISO10646]</a>
-characters.
+characters. These escapes are the equivalent of numeric character
+references in HTML or XML documents (see <a rel="biblioentry"
+href="./refs.html#ref-HTML40">[HTML40], Chapters 5 and 25).</a>
+
+<P>The character escape mechanism should be used when only a few
+characters must be represented this way. If most of a document
+requires escaping, authors should encode it with a more appropriate
+encoding (e.g., if the document contains a lot of Greek characters,
+authors might use ISO 8859-7 or UTF 8).
+
+<P>Intermediate processors using a different character encoding may
+translate these escaped sequences into byte sequences of that
+encoding. <strong>Note.</strong> Intermediate processors must not, on
+the other hand, alter escape sequences that cancel the special meaning
+of an ASCII character.
 
 <P><a href="conform.html#conformance">Conforming user agents</a> must
 correctly map to Unicode all characters in any character encodings
-that they recognize (or they must behave as if they did).
+that they recognize (or they must behave as if they did). 
 
 <P>For instance, "B&amp;W?" may be written as "B\&amp;W\?"  or
-"B\26W\3F". For example, a document transmitted as ISO-8859-1
+"B\26 W\3F". For example, a document transmitted as ISO-8859-1
 (Latin-1) cannot contain Greek letters directly:
 "&#954;&#959;&#965;&#961;&#959;&#962;" (Greek: "kouros") has to be
-written as "\3BA\3BF\3C5\3C1\3BF\3C2". These escapes are thus the CSS
-equivalent of numeric character references in HTML or XML documents
-(see <a rel="biblioentry" href="./refs.html#ref-HTML40">[HTML40],
-Chapters 5 and 25).</a>
+written as "\3BA\3BF\3C5\3C1\3BF\3C2". 
 
 <div class="note"><P>
 <em><strong>Note.</strong>
-The character escape mechanism should be used when only a few
-characters must be represented this way. If most of a
-document requires escaping, authors should encode it
-with a more appropriate encoding (e.g., if the document
-contains a lot of Greek characters, authors might use ISO 8859-7
-or UTF 8).
-</em>
+In <a rel="biblioentry" href="./refs.html#ref-HTML40" 
+class="informref">[HTML40]</a>, 
+numeric character references may appear in "style" attribute
+values but not in the content of the STYLE element. Because of this
+asymmetry, we recommend that authors use the CSS character 
+escape mechanism rather than numeric character references.
+For example, authors should write:</em></p>
+
+<pre class="html-example">
+   &lt;SPAN style="voice-family: D\FCrst"&gt;...&lt;/SPAN&gt;
+</pre>
+
+<P><em>rather than:</em></p>
+
+<pre class="html-example">
+   &lt;SPAN style="voice-family: D&amp;amp;#FC;rst"&gt;...&lt;/SPAN&gt;
+</pre>
 </div>
 
 </BODY>
