[css-text-4] Use 1/8ic spacing for ideograph-alpha/ideograph-numeric w…

…3c#6950

css-text-4/Overview.bs

@@ -8157,10 +8157,17 @@ Inter-script Spacing</h4>
 	when they are directly adjoining on a line,
 	i.e. without any intervening non-zero [=margin=], [=border=], or [=padding=]
 	or intervening characters (such as a quotation mark or a space).
+	The amount of space introduced by these keywords is 1/8 of the CJK advance measure,
+	i.e ''0.125ic''.
 
 	Note: Spacing conventions vary, but values typically range from 1/4ic to as low as 1/8ic,
 	with 1/4ic being more common in historical contexts due to metal type limitations
 	and 1/6ic or thinner being more common in proportional typesetting.
+	Because these spaces are inserted by default
+	(through the initial value, ''text-spacing/normal''),
+	CSS uses 1/8ic in order to be conservative in its interference.
+	A future level of this module may introduce control
+	over the amount of spacing.
 
 <h4 id="fullwidth-collapsing">
 Fullwidth Punctuation Collapsing</h4>