[css-align] Editorial improvements

Author: fantasai

css-align/Overview.bs

@@ -167,11 +167,11 @@ Overview of Alignment Properties</h2>
 	When set on a flex container or grid container,
 	they specify the interpretation of any ''*-self: auto'' used on the items in the container element.
 
-<h2 id='alignment-values'>
-Alignment Values</h2>
+<h2 id='terms'>
+Alignment Terminology</h2>
 
-	All of the alignment properties use a common set of values,
-	defined below.
+	Since this module defines alignment properties for all layout modes in CSS,
+	some abstract terminology is introduced:
 
 	<dl>
 		<dt><dfn export>alignment subject</dfn>
@@ -187,6 +187,34 @@ Alignment Values</h2>
 			The <a>alignment container</a> is the rectangle that the <a>alignment subject</a> is aligned within.
 			This is defined by the layout mode,
 			but is usually the <a>alignment subject</a>’s containing block.
+
+		<dt><dfn export>fallback alignment</dfn>
+		<dd>
+			Some alignments can only be fulfilled in certain situations
+			or are limited in how much space they can consume;
+			for example, ''space-between'' can only operate when there is more than one <a>alignment subject</a>,
+			and baseline alignment, once fulfilled, might not be enough to absorb all the excess space.
+			In these cases a <a>fallback alignment</a> takes effect
+			(as defined below)
+			to fully consume the excess space.
+	</dl>
+
+<h2 id='alignment-values'>
+Alignment Keywords</h2>
+
+	All of the alignment properties use a common set of keyword values,
+	which are defined in this section.
+	Keywords fall into three categories:
+
+	<dl>
+		<dt><a href="#positional-values">positional alignment</a>
+		<dd>These keywords define alignment as an absolute position within the <a>alignment container</a>.
+
+		<dt><a href="#baseline-values">baseline alignment</a>
+		<dd>These keywords define alignment as a relationship among baselines within an <a>alignment context</a>.
+
+		<dt><a href="#distribution-values">distributed alignment</a>
+		<dd>These keywords define alignment as a distribution of space among <a>alignment subjects</a>.
 	</dl>
 
 <h3 id='positional-values'>
@@ -260,7 +288,7 @@ Positional Alignment: the ''center'', ''start'', ''end'', ''self-start'', ''self
 	<p class='issue'>
 		Make it easier to understand the dual-axis nature of "start" and "end" wrt orthogonal flows.
 
-<h3 id='baseline'>
+<h3 id='baseline-values'>
 Baseline Alignment: the ''baseline'' and ''last-baseline'' keywords</h3>
 
 	See [[css-writing-modes-3#intro-baselines]].
@@ -270,6 +298,9 @@ Baseline Alignment: the ''baseline'' and ''last-baseline'' keywords</h3>
 	within a <a>shared alignment context</a>
 	(such as cells within a row or column)
 	by matching up their <a>alignment baselines</a>.
+	If the <a>alignment subject</a>’s position is not fully determined by <a>baseline alignment</a>--
+	or if it has no <a>natural baseline</a> in the appropriate axis--
+	the <a>alignment subject</a> is fallback-aligned insofar as possible while preserving the <a>baseline alignment</a>.
 
 	The baseline alignment keywords are:
 
@@ -290,10 +321,7 @@ Baseline Alignment: the ''baseline'' and ''last-baseline'' keywords</h3>
 			in the <a>first baseline sets</a>
 			of all the boxes in its <a>baseline-sharing group</a>.
 
-			If the <a>alignment subject</a>’s position is not fully determined by <a>baseline alignment</a>,
-			or the box has no <a>natural baseline</a> in the appropriate axis,
-			the content is ''start''-aligned insofar as possible while preserving the <a>baseline alignment</a>.
-			(<a>Alignment subjects</a> that have no inline-level content are thus ''start''-aligned.)
+			The <a>fallback alignment</a> for ''baseline'' is ''start''.
 
 		<dt><dfn>last-baseline</dfn>
 		<dd>
@@ -305,10 +333,7 @@ Baseline Alignment: the ''baseline'' and ''last-baseline'' keywords</h3>
 			in the <a>last baseline sets</a>
 			of all the boxes in its <a>baseline-sharing group</a>.
 
-			If the <a>alignment subject</a>’s position is not fully determined by <a>baseline alignment</a>,
-			or the box has no <a>natural baseline</a> in the appropriate axis,
-			the content is ''end''-aligned insofar as possible while preserving the <a>baseline alignment</a>.
-			(<a>Alignment subjects</a> that have no inline-level content are thus ''end''-aligned.)
+			The <a>fallback alignment</a> for ''baseline'' is ''start''.
 
 			Issue: Should this ''end'' fallback be ''safe'' or ''unsafe''?
 	</dl>
@@ -345,7 +370,7 @@ Distributed Alignment: the ''<content-distribution>/stretch'', ''space-between''
 	to distribute the <a>alignment subjects</a>
 	evenly between the start and end edges of the <a>alignment container</a>.
 	When the <a>alignment subjects</a> cannot be distributed in this way,
-	they behave as their <dfn export>fallback alignment</dfn>.
+	they behave as their <a>fallback alignment</a>.
 	Each distribution value has an associated <<content-position>> as a <a>fallback alignment</a>,
 	but one can alternatively be explicitly specified in the property.