Move scrollMargin details and note to definition section

index.bs

@@ -298,6 +298,20 @@ interface IntersectionObserver {
 		passed to the {{IntersectionObserver}} constructor.  If no
 		{{IntersectionObserverInit/scrollMargin}} was passed to the {{IntersectionObserver}}
 		constructor, the value of this attribute is "0px 0px 0px 0px".
+
+		When calculating a <a>scrollport</a> intersection rectangle for
+		a <a>same-origin-domain target</a>, the rectangle is expanded
+		according to the offsets in the {{IntersectionObserver}}’s {{[[scrollMargin]]}} slot
+		in a manner similar to CSS's 'margin' property,
+		with the four values indicating the amount the top, right, bottom, and left edges, respectively, are offset by,
+		with positive lengths indicating an outward offset.
+		Percentages are resolved relative to the width of the undilated rectangle.
+
+		Note: {{IntersectionObserver/scrollMargin}} affects the clipping of <a for="IntersectionObserver">target</a>
+		by all scrollable ancestors up to and including the <a>intersection root</a>.
+		Both the {{IntersectionObserver/scrollMargin}} and the {{IntersectionObserver/rootMargin}}
+		are applied to a scrollable <a>intersection root's</a> rectangle.
+
 	: <dfn>thresholds</dfn>
 	::
 		A list of thresholds, sorted in increasing numeric order,
@@ -341,19 +355,6 @@ If a <a for="IntersectionObserver">target</a> {{Element}} is clipped by an ances
 <a>intersection root</a>, that clipping is unaffected by
 {{IntersectionObserver/rootMargin}}.
 
-When calculating a <a>scrollport</a> intersection rectangle for
-a <a>same-origin-domain target</a>, the rectangle is expanded
-according to the offsets in the {{IntersectionObserver}}’s {{[[scrollMargin]]}} slot
-in a manner similar to CSS's 'margin' property,
-with the four values indicating the amount the top, right, bottom, and left edges, respectively, are offset by,
-with positive lengths indicating an outward offset.
-Percentages are resolved relative to the width of the undilated rectangle.
-
-Note: {{IntersectionObserver/scrollMargin}} affects the clipping of <a for="IntersectionObserver">target</a>
-by all scrollable ancestors up to and including the <a>intersection root</a>.
-Both the {{IntersectionObserver/scrollMargin}} and the {{IntersectionObserver/rootMargin}}
-are applied to a scrollable <a>intersection root's</a> rectangle.
-
 Note: <a>Root intersection rectangle</a> and <a>scrollport</a> intersection rectangles are not affected by
 <a>pinch zoom</a> and will report the unadjusted <a>viewport</a>, consistent with the
 intent of pinch zooming (to act like a magnifying glass and NOT change layout.)