how can i know if an external application its at the front of max? for example, i'm opening an external application from max in windows and this application goes fullscreen so if you quit you have the max patch behind but for some reason i need to make a bang when you quit the external application the issue is that i need to know when

so can i know what application its the S.O. focused on? (like to know what application (or window) the SO is choosing by control + tab or command + tab)

thanks