“Markup extensions are a XAML concept. In attribute syntax, curly braces ({ and }) indicate a markup extension usage. This usage directs the XAML processing to escape from the general treatment of attribute values as either a literal string or a directly string-convertible value.” (my italics)
See http://msdn.microsoft.com/en-us/library/ms752059.aspx
“When used to provide an attribute value, the syntax that distinguishes a markup extension to a XAML processor is the presence of the opening and closing curly braces ({ and }). The type of markup extension is then identified by the string token immediately following the opening curly brace.
When used in property element syntax, a markup extension is visually the same as any other element used to provide a property element value: a XAML element declaration that references the markup extension class as an element, enclosed within angle brackets (<>). ”
See http://msdn.microsoft.com/en-us/library/ms747254.aspx
XAML-defined markup extensions
There are a number of XAML extensions not specific to WPF. These are usually identified by the prefix x: which is an XML prefix used to map the XAML namespace.
| Extension tag | Description |
| x:Type | Supplies the Type object for the named type. This is used most frequently in styles and templates. |
| x:Static | Produces static values from value-type code entities that are not directly the type of a property's value, but can be evaluated to that type. |
| x:Null | Specifies null as a value for a XAML property. |
| x:Array | Provides support for creation of general arrays in XAML syntax, for cases where the collection support provided by base elements and control models is deliberately not used. |
Nested extension syntax
Extensions can be nested. For example:
<Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}" />
{} Escape Sequence / Markup Extension
To escape curly braces precede with the {} escape sequence, especially where the first character of the property is an opening curly brace. For example:
<Setter Property="SomeProperty" Value="{}{" />
The value of SomeProperty will be set to {.
“The {} escape sequence is frequently required when specifying an XML type that must include a namespace qualifier in a location where XAML markup extension might appear. This includes the beginning of an XAML attribute value, and within a markup extension, immediately after an equal-sign. The following example shows escapes for an XML namespace that appears at the beginning of a XAML attribute value.”
<StackPanel.Resources>
<DataTemplate DataType="{}{http://planetsNS}Planet" >
<StackPanel Orientation="Horizontal">
<TextBlock Width="100" Text="{Binding Path=Element[{http://planetsNS}DiameterKM].Value}" />
<TextBlock Width="100" Text="{Binding Path=Attribute[Name].Value}" />
<TextBlock Text="{Binding Path=Element[{http://planetsNS}Details].Value}" />
</StackPanel>
</DataTemplate>
</StackPanel.Resources>