[css-inline] Restructure initial-letter-align

Author: fantasai

css-inline/Overview.bs

@@ -390,8 +390,8 @@ The 'initial-letter' property does not apply to boxes that are not positioned at
 An <a>initial letter</a> is laid out following the steps outlined below:
 
 <ol>
-	<li>Find font size based on 'initial-letter-align' alignment points and font metrics.
-	Note that no layout information is required in this step.
+	<li>Find the used font size based on its 'initial-letter' size, 'initial-letter-align' alignment points, and font metrics.
+	Note that no layout is required in this step.
 	The font size used for sizing the <a>initial letter</a> contents <em>does not</em> affect its computed 'font-size' property
 	(and therefore has no effect on the computation of ''em'' length values, etc.).
 
@@ -426,39 +426,40 @@ As mentioned earlier, the alignment of initial letters depends on the script use
 
 <pre class="propdef" id="initial-letter-align">
 Name: <dfn id="propdef-initial-letter-align">initial-letter-align</dfn>
-Value: auto | alphabetic | ideographic | margin-box | content-box
-Initial: auto
+Value: border-box? [ alphabetic | ideographic | hebrew ] | border-box
+Initial: alphabetic
 Applies to: <code>::first-letter</code> pseudo elements and inline level first child of a block container
-Inherited: no
+Inherited: yes
 Percentages: N/A
 Media: visual
 Computed value: specified value
 </pre>
 
+This property specifies the alignment points used to size and position an <a>initial letter</a>.
+Two sets of alignment points are necessary:
+the <a>over</a> and <a>under</a> alignment points of the <a>initial letter</a>
+are matched to corresponding <a>over</a> and <a>under</a> points of the surrounding text.
 
-<dl dfn-type="value" dfn-for="initial-letter-align">
-<dt>auto</dt>
-<dd>The user agent selects the value which corresponds to the language of the text. Western languages would default to ''alphabetic'', CJK languages to ''ideographic'', and some Indic languages to ''hanging''. </dd>
-
-<dt>alphabetic</dt>
-<dd>As described above, the cap height of the initial letter aligns with the cap height of the first line of text. The baseline of the initial letter aligns with the baseline of the Nth text baseline.</dd>
-
-<dt>ideographic</dt>
-<dd>The initial letter is centered in the N-line area. 
+Values have the following meanings:
 
-<dt>margin-box</dt>
-<dd>Uses the <a>line-over</a> and <a>line-under</a> margin edges
-as the <a>over</a> and <a>under</a> alignment points, respectively.
-
-<dt>content-box</dt>
-<dd>Uses the <a>line-over</a> and <a>line-under</a> content edges
-as the <a>over</a> and <a>under</a> alignment points, respectively.
-(In most cases, these will correspond to
-the <a>over</a> and <a>under</a> edges of the glyph bounding box.)
+<dl dfn-type="value" dfn-for="initial-letter-align">
+	<dt><dfn>alphabetic</dfn>
+	<dd>Use the alphabetic and cap-height baselines of the surrounding text
+	to align the <a>initial letter</a>.
+	
+	<dt><dfn>ideographic</dfn>
+	<dd>Use the ideographic character face bottom and top edge baselines of the surrounding text
+	to align the <a>initial letter</a>.
+	
+	<dt><dfn>hebrew</dfn>
+	<dd>Use the alphabetic and (as yet theoretical) hebrew hanging baseline of the surrounding text
+	to align the <a>initial letter</a>.
+
+	<dt><dfn>border-box</dfn>
+	<dd>Uses the <a>initial letter box</a>’s <a>line-over</a> and <a>line-under</a> border edges
+	as the <a>over</a> and <a>under</a> alignment points, respectively.
 </dl>
 
-<p class="issue">Input from those knowledgeable about non-Western  typographic traditions would be very helpful in describing the appropriate alignments. More values may be required for this property.</p>
-
 <div class="example">
 The vertical writing mode example from <a href="#f2">Figure 2</a> could be coded as:
 
@@ -468,19 +469,48 @@ span.initial {
   initial-letter-alignment: ideographic;
 }
 </pre>
+</div>
 
+Except when ''border-box'' is specified,
+the alignment points of the <a>initial letter</a>
+are automatically determined from its contents:
+	<ol>
+		<li>If the <a>initial letter</a> is an atomic inline,
+		use its <a>over</a> and <a>under</a> content-box edges.
+		<li>Else if the <a>initial letter</a> contains any character from the Han, Hangul, Kana, or Yi <a>Unicode scripts</a>,
+		use the ideographic character face bottom and top edge baselines.
+		<li>Else if the <a>initial letter</a> contains any character from the Hebrew <a>Unicode scripts</a>,
+		use the ideographic character face bottom and top edge baselines.
+		<li>Else use the alphabetic and cap-height baselines.
+	</ol>
+
+Note: The ordering of keywords in this property is fixed in case ''border-box''
+is expanded to ''[ border-box | alphabetic | ideographic | hebrew ]''
+to allow explicitly specifying the <a>initial letter</a>’s alignment points. 
+
+<h4 id="initial-letter-align-defaults">
+UA Default Stylesheet for 'initial-letter-align'</h4>
+
+In order to provide the better behavior by default,
+UAs must include in their default UA style sheet the following rules:
 
-</div>
+<pre>
+[lang=zh], [lang=ja], [lang=ko], [lang=ii] {
+  initial-letter-align: ideographic;
+}
+[lang|=iw], [lang|=yi], [lang|=lad], [lang|=jrb] {
+  initial-letter-align: hebrew;
+}
+</pre>
 
-If 'initial-letter' is applied to an image or other atomic element that does not provide the necessary alignment information, the alignment points for the atomic inline must be synthesized from the content edges.
+Issue: We don't have a way to do subtag selection with attr selectors.
+(It's a feature of '':lang()'' in Selectors 4,
+but we don't want to use that because we want to hit the language root,
+not all of the descendant elements.)
+These selectors should also include the relevant script subtags.
 
-Note: For 'vertical-align', the alignment points of an atomic inline are synthesized from the margin edges. [[CSS3-WRITING-MODES]]
+</div>
 
-<!--
-  ]]]]]]]]]]]]
-  ]]]]]=======
-  ============
--->
 <h3 id="sizing-initial-letters">
 Sizing Initial Letters</h3>