https://learn.microsoft.com/ja-jp/dotnet/api/system.windows.automation.scrollpattern.horizontalviewsizeproperty?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-10.0
ScrollPattern.HorizontalViewSizeProperty Field (System.Windows.Automation) | Microsoft Learn
Identifies the HorizontalViewSize property.
field systemwindowsautomationmicrosoftlearn