Locating files associated with an external

We have developed an external that embed some resource files with it. The external is typically installed in the /Applications/Max6/Cycling '74/msp-externals folder, but this location may be changed by the user (if he/she wants to have this external be distributed with a give patch for instance)

What is the proper way to locate the folder from where the given external has been loaded in Max? So that the final complete path of the associated resources can be correctly be found?

Thanks.