This is another type of XAML syntax that allows you to define the property as an element. This is often used when you cannot assign the value of the property within quotes. If we take the previous example, the text Click Here can be assigned to the button content easily. But, when you have another element or a composite property value, you cannot write those within the quotes. For this, XAML introduces Property Element syntax to help you to define the property value easily.
It starts with <element.PropertyName> and ends with </element.PropertyName>. The following example demonstrates how to assign a color to a button background with a SolidColorBrush object:
<Button>
<Button.Background>
<SolidColorBrush Color="Red" />
</Button.Background>
</Button>