StringBuilder substring?

Well, it may have been obvious for many, but I had no idea. Whenever I was writing a piece of code that uses a StringBuilder I was terribly upset by the lack of a substring method.

It was there all along, only it is the ToString method. You give it the startIndex and length and you're set.

Looking at the source, I see that in .Net 1.1 this method is only a normal Substring on the internal string used by the string builder. In Net 2.0, the method uses a InternalSubStringWithChecks internal method of the string class, which is using a InternalSubString unsafe method that seems to be more basic and thus faster.