What does "This being...." mean here?

This being Silverlight, you’d expect there to be some way to get the XAML representation of the selected text—and you’d be right.

What does the clause 'This being Silverlight', and especially the meaning of the word 'being' in the following sentence?

"This being Silverlight" in the context means "Because this is Silverlight" or "Since this is Silverlight"

Silverlight is a Microsoft development platform. The clause could be rewritten:

Since this is Silverlight...

While @Josek is right, I think the phrase has a more subtle connotation. "This being x" is an expression that implies some innate knowledge about the nature of object x which leads, almost as a corollary, to the second statement.

"This being Silverlight, you’d expect there to be some way to get the XAML representation of the selected text—and you’d be right."

Could then be rephrased, "Since you are familiar with the nature of Silverlight you’d expect there to be some way to get the XAML representation of the selected text—and you’d be right, ."