Windows Presentation Foundation (WPF) Question:

The typical reason for specifying a read-only dependency property is that these are the properties that is used to determine the state, but where the state is defined in a multitude of factors. A typical example for a read-only property is IsMouseHover

This example shows how to 'register' an attached property as read-only. You can use dependency properties on any 'DependencyObject' types.

[C#]
public static readonly DependencyProperty IsBubbleSourceProperty = DependencyProperty.RegisterReadOnly(
"IsBubbleSource",
typeof(Boolean),
typeof(AquariumObject),
new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender)
);