If you are using TextTransform.exe with the -a option for passing a parameter to a directive processor, and you have created your own directive processor, the directive processor must call the ITextTemplatingEngineHost.ResolveParameterValue(string,string,string) method in order to get access to the parameters.
Parameters specified within the directive processor declaration on a text template are available separately to the directive processor by examining the "arguments" parameter of the DirectiveProcessor.ProcessDirective(string directiveName, IDictionary<string,string> arguments) method.