What perflow variable in an APM Per Request policy holds the URL being requested?

Does anyone know what the best way is to look up the current URL in a per request policy in APM? I want to branch based on URL in a per request policy (using an APM empty object), but I’m not sure what variable that is stored in. There is this variable, perflow.category_lookup.result.url, but it only gets populated if you do a category lookup, and I am not doing category lookups in this policy. So I’m looking for something else… any ideas?