Thanks a lot for you help. You’re absolutely right ThnicknessConverter does the job.
It has internal method FromString that include the code bellow:

switch (index)
{
case 1:
return new Thickness(numArray[0]);

case 2:
return new Thickness(numArray[0], numArray[1], numArray[0], numArray[1]);

case 4:
return new Thickness(numArray[0], numArray[1], numArray[2], numArray[3]);
}

Rune has it right. Some properties of WPF objects have implicit converters attached to them (based on type). This allows the input string to take several different forms without having to specify a converter in XAML for each use.

The converter at work here is a ThicknessConverter which parses the input string and attempts to map the values given in the string to one of the Thickness object constructor overloads.

For more information take a look at http://msdn.microsoft.com/en-us/library/ms752059.aspx#typeconverterenabled

Sam.

I am by no means a WPF guru, but I am learning as well.

Just like with LINQ, the compiler does a LOT of magic behind the scenes when churning XAML into something binary. The XAML you create can be quite different from the actual object structure the compiler builds for you. So my guess would be that something tells the compiler that “x y” must be the same as “x y x y”..

Rune