They are guides, like roof pivot lines and fill handles. It is possible to write a library part (detail marker subtype) that will do this. (Not too difficult if you are fairly profficient with GDL; but the detail marker subtype has some maddening quirks.)
I don't know if any of the included detail marker types offer this option. I tried them out just long enough to find that they didn't work the way I wanted; so I immediately wrote some of my own and haven't used any of the included ones since.
I have one marker that shows the rectangular bounds of the detail area (see attached). It is presently too customized to our practice for general release, but, if enough people are interested, I might be able to find the time to make the necessary modifications. Any one who would like a copy should please e-mail me privately at the address below.