https://learn.microsoft.com/fr-fr/dotnet/api/system.windows.markup.trimsurroundingwhitespaceattribute?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-9.0
TrimSurroundingWhitespaceAttribute Class (System.Windows.Markup) | Microsoft Learn
Indicates to XAML processors that the whitespace surrounding elements of the type in markup should be trimmed when serializing.
class systemwindowsmarkupmicrosoftlearn