Layout

WPF shapes layout by using different containers.
WPF window can only have one element, so if need to put more, use a container. Containers can be nested to create complex layout.
Layout process:
- measure: loop through child elements and identify preferred size
- arrange: place child elements
GridSplitter:
DockPanel:
https://learn.microsoft.com/en-us/dotnet/desktop/wpf/advanced/layout?view=netframeworkdesktop-4.8