navigating-mewui-tree

## Element Hierarchy ``` Element (base) └─ UIElement (input, visibility, focus) └─ FrameworkElement (sizing, margin, alignment) ├─ Panel (multi-child: StackPanel, Grid, Canvas, DockPanel) ├─ Control (themed elements: Button, Label, TextBox) │ ├─ ContentControl (single child: Window) │ └─ Border (decorator) └─ ... ``` --- ## Parent-Child Relationships ```csharp // Every element has one parent Element? parent = element.Parent; // Multi-child (Panel) panel.Add(child); // Sets child.Parent = panel panel.Remove(child); // Sets child.Parent = null panel.Children; // IReadOnlyList<Element> // Single-child (ContentControl, Border) contentControl.Content = child; // Element? type, sets child.Parent border.Child = child; // UIElement? type ``` --- ## Tree Traversal ```csharp // Find visual root (usually Window) Element? root = element.FindVisualRoot(); // Check ancestry bool isChild = element.IsDescendantOf(ancestor); bool isParent = element.IsAncestorOf(descendant); // Also available // Find ancestor of type static T? FindAncestor<T>(Element element) where T : Element { for (var cur = element.Parent; cur != null; cur = cur.Parent) if (cur is T match) return match; return null; } ``` Note: `VisualTree.Visit()` exists but is `internal` - use FindVisualRoot/IsDescendantOf for external code. --- ## IVisualTreeHost (Internal) Interface for elements with children (internal API): ```csharp intern...