[css-sizing-3] Define terms 'intrinsic size' and 'intrinsic size contribution', which we use a lot but don't <dfn> anywhere.

Author: fantasai

css-sizing-3/Overview.bs

@@ -233,6 +233,13 @@ Auto Box Sizes</h3>
 
 			Note: This is called the “shrink-to-fit” width in <a href="https://www.w3.org/TR/CSS2/visudet.html#float-width">CSS2.1§10.3.5</a>
 			and <a href="https://www.w3.org/TR/css3-multicol/#pseudo-algorithm">CSS Multi-column Layout § 3.4</a>.
+
+		<dd><dfn>intrinsic size</dfn>
+		<dd>
+			A <a>max-content size</a> or <a>min-content size</a>,
+			i.e. a size arising primarily from the size of the content.
+			(Some uses of this term may refer also to sizes
+			derived primarily from one of these two sizes.)
 	</dl>
 
 <h3 id='contributions' dfn export lt="intrinsic size contribution">
@@ -246,6 +253,11 @@ Intrinsic Size Contributions</h3>
 		<dt><dfn lt="min-content contribution|min-content inline-size contribution|min-content block-size contribution">min-content contribution</dfn>
 		<dd>
 			The size that a box contributes to its <a>containing block</a>'s <a>min-content size</a>.
+
+		<dd><dfn>intrinsic size contribution</dfn>
+		<dd>
+			A <a>max-content contribution</a>, <a>min-content contribution</a>,
+			or similarly-calculated content-based size contribution.
 	</dl>
 
 	Intrinsic size contributions are based on the <a>outer size</a> of the box;