How to add a new class as an input parameter in a idl file

Hi,

How can I add a new class as an input parameter in a idl file:
For example, I add this in a idl file

 void setMyClass(in MyClass myclass);

When I compile it, I get the following error:

../../../../dist/bin/xpidl -m header -w -I/home/firefox/mozilla/
embedding/c.omponents/windowwatcher/public -I../../../../dist/idl -o
_xpidlgen/nsIPromptService /home/firefox/mozilla/embedding/components/
windowwatcher/public/nsIPromptService.idl
/home/firefox/mozilla/embedding/components/windowwatcher/public/
nsIPromptService.idl:383: 'MyClass' undeclared identifier

Can you please tell me how can I 'define' MyClass in idl file?

Thank you