[css-rhythm] Handle truncated margins. #1260

Author: fantasai

css-rhythm/Overview.bs

@@ -245,6 +245,15 @@ Specifying Alignment: the 'block-step-align' property {#block-step-align}
 			is inserted on the <a>end</a> side of the box.
 	</dl>
 
+	In all cases,
+	additional spacing cannot be added to margins
+	that are truncated due to unforced page breaks
+	(see [[CSS3-PAGE]]);
+	therefore if 'block-step-insert' is ''margin'',
+	all extra space derived from applying 'block-step-size'
+	must be inserted on the opposite side of the box
+	(regardless of 'block-step-align').
+
 Rounding Method: the 'block-step-round' property {#block-step-round}
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