Changes in documentation for making value as content property for setter (#9581)

Author: Anjali

xml/System.Windows/Setter.xml

@@ -46,7 +46,9 @@
 ## Remarks  
  <xref:System.Windows.Style>s and the different types of triggers (classes that inherit from <xref:System.Windows.TriggerBase>) use <xref:System.Windows.Setter>s to apply property values.  
   
- Note that you must specify both the <xref:System.Windows.Setter.Property%2A> and <xref:System.Windows.Setter.Value%2A> properties on a <xref:System.Windows.Setter> for the setter to be meaningful. If one or both properties are not set, an exception will be thrown.  
+You must specify both the <xref:System.Windows.Setter.Property%2A> and <xref:System.Windows.Setter.Value%2A> properties on a <xref:System.Windows.Setter> for the setter to be meaningful. In .NET 8 and earlier versions, an exception is thrown if one or both properties aren't set.  
+
+  **Content Model:** In .NET 9 and later versions, the content property for <xref:System.Windows.Setter> is <xref:System.Windows.Setter.Value%2A>, and it's optional to specify <xref:System.Windows.Setter.Value%2A> as an attribute.