How to add System.Text.RegularExpressions to references ? C#

[icebox]

I guess no other info is required, the questions is the title.

This namespace seems to be not in the "default" folders of windows, for namespaces. How can I add it ?

SOLVED:
Haven't thought of using System.Text.RegularExpression.MatchCollection

Still now, I have another problem, how can I get the {-Page.Dom-} as a variable in the C# code ?