SQL Reporting Services - Expression language?

I'm starting to use SQL Reporting Services. I've got some textboxes that I want to format nicely for an address, for example.

Unit
Street
City Region PostalCode
Country

All this needs to be in one textbox. If Unit or Street is null, then there should be no blank line.

So, I've got an expression in my Textbox Value property:

=Fields!Unit.Value + IIf(Fields!Unit.Value=““,““,chr(13) + chr(10)) + Fields!Street.Value + chr(13) + chr(10) + Fields!City.Value + “ “ + Fields!Region + “  “ + Fields!PostalCode.Value

It sorta works, I just tried out the chr(13) + Chr(10) bit and it does put in a carriage return. I'm now seeing if I can use IsNull() [first crack at that is that it doesn't exist] and IIf() does exist.

My question to the blogsphere is this: what expression language is used in SQL RS? VBA? It doesn't look like .NET. Is there a reference anywhere as to what functions are available?

Mike