The Silk Performer code-generation engine also checks the virtual user class of all defined random-variable custom attributes. For each random variable, the corresponding random-variable definition is declared in the BDL script.
Currently these variables are of no real use, neither on the BDL side or the .NET side. If you use one of the Bdl.GetRandom functions, the definition of the random variable is read from the metadata information of the .NET code, not from the BDL file. That means that if you change the random variable definition in BDL it will not have any effect on the .NET code as it still must have the definition from the custom attributes. This behavior will be adjusted in future versions so that you will be able to change settings in the BDL script and have the executing .NET code receive those random values based on the BDL settings.