Say window where these comments still say frame

Lengths became lengths of the window when the frame did, and `Part::From`'s
own documentation still described its spans as frame lengths -- which is
what the scroll above read them as.

core/src/ui/painter.rs

@@ -541,7 +541,7 @@ impl PrimitiveLike for &TextureHandle {
 /// method's `impl` block is where a `Painter`'s own boxes are, so it takes
 /// only what the child was asked with.
 impl Painter<'_> {
-    /// Frame ranges are already ranges on the window and combine directly.
+    /// Window ranges are already about the one unit and combine directly.
     /// A frame pin becomes this widget's own frame wherever a length of it
     /// is what reached the child; where only pixels did, no length of this
     /// frame can change the child's and the pin stops here.
@@ -563,8 +563,8 @@ impl Painter<'_> {
         let mut result = LayoutHolds::ANY;
         for axis in AXES {
             let n = axis as usize;
-            // Every frame range is already a range on the window: the
-            // widget's own read converted through its frame exactly once.
+            // Every read became pixels against the window, so a range on
+            // it is already in this widget's terms.
             result.window[n] = holds.window[n];
             let reaches = narrow[n].is_none()
                 && !matches!(place[n].part(), Part::Sized(_))
@@ -596,10 +596,10 @@ impl Painter<'_> {
                         _ => self.extent.axis(axis).len(),
                     });
                 }
-                // Its box is a part of this widget's frame, or a length of
-                // it decided here: a length of the frame is all that reaches
-                // it, so what it holds for is a range on the frame and none
-                // of it on this widget's own box.
+                // Its box is a length this widget decided, from its own
+                // frame or from a sibling's answer: no length of this
+                // widget's box reaches it, so what it holds for is a range
+                // on the window and none of it on that box.
                 _ => {
                     result.window[n] =
                         result.window[n].and(holds.extent[n].through(extent.axis(axis).len()));