[css-grid-1] Clarify that the argument to fit-content() is interpreted as a track sizing function and not some other mysterious and undefined thing. #3583

Author: fantasai

css-grid-1/Overview.bs

@@ -1519,7 +1519,8 @@ Track Sizes</h4>
 			<code>min(<var>minimum</var>, max(<var>limit</var>, ''max-content''))</code>,
 			where <var>minimum</var> represents an ''grid-template-columns/auto'' minimum
 			(which is often, but not always, equal to a ''min-content'' minimum),
-			and <var>limit</var> is the argument to ''fit-content()''.
+			and <var>limit</var> is the <a>track sizing function</a>
+			passed as an argument to ''fit-content()''.
 			This is essentially calculated as the smaller of
 			''minmax(auto, max-content)'' and ''minmax(auto, <var>limit</var>)''.
 	</dl>