[css-navigation-1] Describe how to: URL changes during redirects.

Author: dbaron

css-navigation-1/Overview.bs

@@ -130,6 +130,8 @@ as follows:
 			[=URL pattern/match|matches=]
 			the [=navigation location URL pattern=] of <<navigation-location>>.
 
+			NOTE: This part handles <code>from:</code> when it matches in the old page.
+
 		* its [=activation=] is non-null,
 			the document's [=has been revealed=] is false or
 			was false at the start of the current [=task=],
@@ -139,16 +141,36 @@ as follows:
 			[=URL pattern/match|matches=]
 			the [=navigation location URL pattern=] of <<navigation-location>>.
 
+			NOTE: This part handles <code>from:</code> when it matches in the new page.
+
 	: to: <<navigation-location>>
 	:: The result is true if
 		the [=document's navigation API=] of the document
 		is non-null, and either:
 
 		* its [=ongoing navigate event=] is non-null,
-			and its {{NavigateEvent/destination}}'s
-			{{NavigationDestination/url}}
+			and the [=current to url=]
 			[=URL pattern/match|matches=]
-			the [=navigation location URL pattern=] of <<navigation-location>>.
+			the [=navigation location URL pattern=] of <<navigation-location>>,
+			where the <dfn>current to url</dfn> is defined as:
+
+			* if the {{pageswap}} event has fired since that navigation began,
+				and its {{PageSwapEvent/activation}} was non-null,
+				and that {{PageSwapEvent/activation}}'s
+				{{NavigationActivation/entry}}'s
+				{{NavigationHistoryEntry/url}} is non-null,
+				then that
+				{{NavigationHistoryEntry/url}}.
+
+				NOTE: This part <em>does</em> expose the result of redirects.
+
+				ISSUE: Is the final "non-null" check needed?
+
+			* otherwise, the [=ongoing navigate event=]'s
+				{{NavigateEvent/destination}}'s
+				{{NavigationDestination/url}}
+
+				NOTE: This part does <em>not</em> expose the result of redirects.
 
 			ISSUE: This assumes that the [=ongoing navigate event=]
 			and the [=transition=] have the same lifetime,
@@ -160,6 +182,8 @@ as follows:
 			we could probably define this more like "from" above.
 			But which lifetime is the one we want?
 
+			NOTE: This part handles <code>to:</code> when it matches in the old page.
+
 		* its [=activation=] is non-null,
 			the document's [=has been revealed=] is false or
 			was false at the start of the current [=task=],
@@ -169,18 +193,17 @@ as follows:
 			[=URL pattern/match|matches=]
 			the [=navigation location URL pattern=] of <<navigation-location>>.
 
-		TODO: Update this definition to handle redirects better.
-		In particular, we'd like the ''to:'' URL to change
-		at only a single time,
-		from the original URL of the navigation to the final one.
-		There is already a well-defined definition and processing model
-		that we can depend on.
+			NOTE: This part handles <code>to:</code> when it matches in the new page.
 
 	ISSUE: The above definitions of from and to apparently don't work right
 	if you start a same-document navigation (e.g., with {{History/pushState}})
 	in the middle of a cross-document navigation.
 
-	ISSUE: Improve integration with [=has been revealed=] rather than monkeypatching it.
+	ISSUE: Generally improve integration with the HTML spec for these definitions,
+	instead of monkeypatching.
+	This includes the interaction with [=has been revealed=]
+	and the interaction with the {{pageswap}} event,
+	and other things where this section links to non-exported definitions.
 
 : <<general-enclosed>>
 ::