Replace placement calls with region nodes

tests/generated.rs

@@ -1,10 +1,9 @@
 //! Random trees, checked against building the same tree cold.
 //!
-//! A frame reaches its layout by keeping most of the last one: slots
-//! rewritten, some widgets drawn again, the rest untouched. The property here
-//! is that what comes out is the tree a cold start would have produced, so
-//! anything the retained path carried over that it should not have shows up
-//! as a difference in somebody's box.
+//! A frame reaches its layout by keeping most of the last one: movable regions
+//! or primitive boxes rewritten, some widgets drawn again, the rest untouched.
+//! The result must be the tree a cold start would have produced, so anything
+//! wrongly retained shows up as a difference in somebody's box.
 //!
 //! `iris::random` grows the tree and `examples/random.rs` draws one. A seed is
 //! the whole reproduction; `a_long_run_of_seeds_agrees` is the ignored sweep
@@ -220,8 +219,8 @@ fn describe(id: WidgetId, h: &Harness) -> String {
 }
 
 /// Every widget in one tree against the matching widget in the other. A
-/// mismatch prints the widget's ancestry, marking the ones that own a slot,
-/// since where two trees disagree is rarely where the cause is.
+/// mismatch prints the widget's ancestry, marking region nodes, since where
+/// two trees disagree is rarely where the cause is.
 fn assert_same(seed: u64, what: &str, warm: (&Harness, &Tree), cold: (&Harness, &Tree)) {
     let ((wh, wt), (ch, ct)) = (warm, cold);
     assert_eq!(wt.ids.len(), ct.ids.len(), "seed {seed}: different trees");
@@ -243,11 +242,11 @@ fn assert_same(seed: u64, what: &str, warm: (&Harness, &Tree), cold: (&Harness,
             let mut at = Some(w);
             while let Some(id) = at {
                 let active = &wh.render.active[&id];
-                let slot = match active.move_idx == active.parent_move {
+                let node = match active.move_idx == active.parent_move {
                     true => "",
                     false => "*",
                 };
-                chain.push(format!("{}{slot}", describe(id, wh)));
+                chain.push(format!("{}{node}", describe(id, wh)));
                 at = active.parent;
             }
             println!(