https://learn.microsoft.com/zh-cn/dotnet/api/system.windows.automation.provider.itextprovider.documentrange?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-10.0
ITextProvider.DocumentRange Property (System.Windows.Automation.Provider) | Microsoft Learn
Gets a text range that encloses the main text of a document.
property systemwindowsautomationprovidermicrosoft