[css-inline] Make sure not to regress SVG coordinate placement of text in vertical writing modes.

Author: fantasai

css-inline/Overview.bs

@@ -72,6 +72,9 @@ Dominant Baselines: the 'dominant-baseline' property</h3>
 			when 'text-orientation' is ''sideways'', ''sideways-right'', or ''sideways-left''.
 			equivalent to ''dominant-baseline/central'' in <i>vertical writing modes</i>
 			when 'text-orientation' is ''mixed'' or ''upright''.
+			
+			In SVG text, the origin point of glyphs is always handled as for ''dominant-baseline/central''
+			in <a>vertical writing modes</a>.
 
 		<dt><dfn>text-bottom</dfn>
 		<dd>