Is the aqString object available in TC Version 6.30.xxx?

I'm writing script code in C# script but the aqString object doesn't appear to be available.  It doesn't come up in the "intellisense".  If I just put it in anyway the script engine obviously throws an error.  

I am using TC version 6.30.327.5

If this object is not available is there another that allows some of the same string operations?

If aqString is available can you tell me how to "enable" it?  

Thanks!