[css-align] Clarify that boxes not in a shared alignment context can't baseline-align.

Author: fantasai

css-align/Overview.bs

@@ -298,9 +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>.
+	If an <a>alignment subject</a>’s position is not fully determined by <a>baseline alignment</a>
+	it and the other participants in its <a>baseline-sharing group</a>
+	are fallback-aligned insofar as possible while preserving their <a>baseline alignment</a>.
 
 	The baseline alignment keywords are:
 
@@ -362,6 +362,9 @@ Baseline Alignment: the ''baseline'' and ''last-baseline'' keywords</h3>
 	Note: The 'vertical-align' property will also need a ''first-baseline'' value
 	because per CSS2.1 for inline blocks, ''baseline'' is equivalent to ''last-baseline''.
 
+	If a box has no <a>natural baseline</a> in the appropriate axis
+	or does not belong to a <a>shared alignment context</a>,
+	then the <a>fallback alignment</a> is used.
 
 <h3 id='distribution-values'>
 Distributed Alignment: the ''<content-distribution>/stretch'', ''space-between'', ''space-around'', and ''space-evenly'' keywords</h3>
@@ -1433,8 +1436,12 @@ Baseline Alignment Terminology</h3>
 		<li>flex items in the same flex line, along the flex container's main axis
 	</ul>
 
-	Note: The inline-level boxes on a line box also share an alignment context and participate in a baseline-sharing group;
-	however this is detailed in the CSS Inline Layout module, not here.
+	Note: Conceptually,
+	the inline-level boxes on a line box also share a self-alignment context
+	and participate in a baseline-sharing group;
+	however they only baseline-align in response to the 'vertical-align' property,
+	not any of the properties defined in this module.
+	See [[CSS-INLINE-3]].
 
 	Boxes in a <a>baseline-sharing group</a> are aligned to each other
 	using their <dfn export>alignment baseline</dfn>.