<===> file1.hrx
<=====> nested-file1.hrx
This is a HRX file nested within a HRX file.
<=====> nested-file2.hrx
You can tell it's not part of the outer file because the boundaries are longer.
<===> file2.hrx
<=> nested-file1.hrx
Inner files can also contain shorter boundaries...
<=> nested-file2.hrx
...as long as they don't contain the outer file's boundary.