Enable XAML preview for WPF
When this option is enabled, XAML files that contain WPF UI markup will have a preview area alongside the text editor. Buttons in the top right corner of the editor will let you choose how to place the preview within the editor tab.
Otherwise, such files will open as text documents.
Automatically show preview for supported WPF files
When this option is enabled, a preview area will be shown in XAML files that contain WPF UI markup as soon as you open them.
Default XAML editor layout
These options let you choose how to display the preview pane relative to the editor pane for the newly opened XAML forms. If you change the orientation of the preview for a specific document, JetBrains Rider will remember your choice.