[css-overflow-3][editorial] Improvements to scrolling terminology section structure

Author: fantasai

css-overflow-3/Overview.bs

@@ -234,8 +234,9 @@ Scrolling Overflow</h3>
 	(through which the <a>scrollable overflow area</a> can be viewed)
 	coincides with its padding box,
 	and is called the <dfn export>scrollport</dfn>.
-	A box’s <dfn export>nearest scrollport</dfn>
-	is the [=scrollport=] of its nearest [=scroll container=] ancestor.
+	A box’s <dfn export>nearest scroll container</dfn>
+	is the its nearest [=scroll container=] ancestor in the [=containing block chain=].
+	(See [[#overflow-properties]] for control over whether a box clips or scrolls its overflow.)
 
 	Scrolling operations can be initiated by the user
 	(for example, by manipulating a scrollbar, swiping a touchscreen, or using keyboard controls)
@@ -262,12 +263,6 @@ Scrolling Overflow</h3>
 	Unless otherwise specified,
 	it is the [=block-start=] [=inline-start=] corner of the [=scrollable overflow rectangle=].
 	(For example, in a [=flex container=] it is the [=main-start=] [=cross-start=] corner.)
-	Unless otherwise adjusted
-	(e.g. [[css-align-3#overflow-scroll-position|by content alignment]] [[css-align-3]]),
-	the area beyond the [=scroll origin=] in either axis
-	is considered the <dfn export>unreachable scrollable overflow region</dfn>:
-	content rendered here is not accessible to the reader,
-	see [[#scrollable]].
 	A [=scroll container=] is said to be scrolled to its [=scroll origin=]
 	when its [=scroll origin=] coincides with the corresponding corner of its [=scrollport=].
 	This [=scroll position=], the <dfn export>scroll origin position</dfn>,
@@ -290,6 +285,13 @@ Scrolling Overflow</h3>
 	or away from the [=scroll origin=] is not defined.
 	Should each API define its coordinate model?
 
+	Unless otherwise adjusted
+	(e.g. [[css-align-3#overflow-scroll-position|by content alignment]] [[css-align-3]]),
+	the area beyond the [=scroll origin=] in either axis
+	is considered the <dfn export>unreachable scrollable overflow region</dfn>:
+	content rendered here is not accessible to the reader,
+	see [[#scrollable]].
+
 	The root viewport, which scrolls the page [=canvas=],
 	uses the <a>principal writing mode</a> for determining
 	its [=scroll origin=] and [=initial scroll position=].