diff --git a/crates/egui-winit/src/lib.rs b/crates/egui-winit/src/lib.rs
index 22cc61745..52b7e7182 100644
--- a/crates/egui-winit/src/lib.rs
+++ b/crates/egui-winit/src/lib.rs
@@ -52,7 +52,9 @@ pub struct EventResponse {
 
 // ----------------------------------------------------------------------------
 
-/// Handles the integration between egui and winit.
+/// Handles the integration between egui and a winit Window.
+///
+/// Instantiate one of these per viewport/window.
 pub struct State {
     start_time: web_time::Instant,
     egui_input: egui::RawInput,
@@ -733,12 +735,13 @@ impl State {
             cursor_icon,
             open_url,
             copied_text,
-            events: _,                    // handled above
+            events: _,                    // handled elsewhere
             mutable_text_under_cursor: _, // only used in eframe web
             text_cursor_pos,
             #[cfg(feature = "accesskit")]
             accesskit_update,
         } = platform_output;
+
         self.current_pixels_per_point = egui_ctx.input_for(viewport_id, |i| i.pixels_per_point); // someone can have changed it to scale the UI
 
         self.set_cursor_icon(window, cursor_icon);
diff --git a/crates/egui/src/context.rs b/crates/egui/src/context.rs
index affb0dd92..93d101908 100644
--- a/crates/egui/src/context.rs
+++ b/crates/egui/src/context.rs
@@ -143,8 +143,10 @@ struct ViewportState {
     /// State related to repaint scheduling.
     repaint: ViewportRepaintInfo,
 
+    // ----------------------
     // The output of a frame:
     graphics: GraphicLayers,
+    // Most of the things in `PlatformOutput` are not actually viewport dependent.
     output: PlatformOutput,
     commands: Vec<ViewportCommand>,
 }
diff --git a/crates/egui/src/data/output.rs b/crates/egui/src/data/output.rs
index 360de3a11..2e94b5f99 100644
--- a/crates/egui/src/data/output.rs
+++ b/crates/egui/src/data/output.rs
@@ -98,6 +98,9 @@ pub struct PlatformOutput {
     /// Iff `Some`, the user is editing text.
     pub text_cursor_pos: Option<crate::Pos2>,
 
+    /// The difference in the widget tree since last frame.
+    ///
+    /// NOTE: this needs to be per-viewport.
     #[cfg(feature = "accesskit")]
     pub accesskit_update: Option<accesskit::TreeUpdate>,
 }