Self-review fixes.

doc/widget_development.md

@@ -43,7 +43,25 @@ returned on a call to the **Options** method aren't static, but depend on the
 user data provided to the widget, the widget **must** protect against the
 scenario where the infrastructure provides a canvas that doesn't match the
 returned options. This is because the infrastructure cannot guarantee the user
-won't change the inputs between calls to **Options** and **Draw**.
+won't change the data between calls to **Options** and **Draw**.
+
+A widget can draw a character indicating that a resize is needed in such cases:
+
+```go
+func (w *Widget) Draw(cvs *canvas.Canvas) error {
+  min := w.minSize() // Output depends on the current state.
+  needAr, err := area.FromSize(min)
+  if err != nil {
+    return err
+  }
+  if !needAr.In(cvs.Area()) {
+    return draw.ResizeNeeded(cvs)
+  }
+
+  // Draw the widget.
+  return nil
+}
+```
 
 If the container configuration results in a canvas larger than **MaximumSize**
 the canvas will be limited to the specified size. Widgets can either specify a

widgetapi/widgetapi.go

@@ -85,10 +85,11 @@ type Widget interface {
 	// size, etc.
 	//
 	// Most widgets will return statically compiled options (minimum and
-	// maximum size, etc.). If the returned options depend on runtime state
+	// maximum size, etc.). If the returned options depend on the runtime state
-	// (e.g. the user data provided to the widget), the widget cannot depend on
+	// of the widget (e.g. the user data provided to the widget), the widget
-	// the infrastructure to no call the Draw method with a canvas that doesn't
+	// must protect against a case where the infrastructure calls the Draw
-	// meet the requested options. This is because the data in the widget might
+	// method with a canvas that doesn't meet the requested options. This is
-	// change between calls to Options and Draw.
+	// because the data in the widget might change between calls to Options and
+	// Draw.
 	Options() Options
 }