SmartCrawl] Expand Macros

I would like to know how to use the expand function in the Macros for SmartCrawl. class_wds_macro.php has a function called expand, I just don't know how I can call that in my function.php to use it. I could not find anything in the documentation about that. I would like to add a macro called %%metroarea%% in the meta descriptions for pages. Please advice.