[css-align-3] Percentage gaps resolve to zero in indefinite containers, per WG resolution. #509

Author: fantasai

css-align-3/Overview.bs

@@ -1637,6 +1637,11 @@ Row and Column Gutters: the 'row-gap' and 'column-gap' properties</h3>
 			see subsections below for details.
 
 			Negative values are invalid.
+			Percentages resolve to zero
+			when specified against an <a>indefinite size</a>
+			(such as the <a>logical width</a> of a float
+			or the ''height/auto'' <a>logical height</a>
+			of a <a>block-level</a> <a>grid container</a>).
 
 		: <dfn>normal</dfn>
 		:: The ''gap/normal'' represents a UA-dependent length on <a>multi-column elements</a>,