>When I am looking at the report form file how do I know (how does foxpro know) which records in the FRX file (which fields in the reports) are in the detail band?

Don,

First, FoxPro calculates position and height of each band in the report. In the process it addes 1979.16666666 to the height of each band to account for band separator you see in the Report Designer. After that position of each object is compared to the calculated start and end of the each band. I would recomend that you download Frx2Word to see how it's done.