DSPDBR outfile question

Can someone explain these two fields in the DSPDBR outfile (created from system file QADSPDBR)?
* WHJDIL Ordinal number of position in the JFILE list
* WHJREF Join reference number
1) What is the difference between these two fields? Guessing that, per the description, WHJDIL refences the JFILE keyword and WHJREF references the JOIN keyword. But...
2) Why is WHJDIL zero for dependent files that are join logical files? WHJREF's values are what I imagine WHJDIL should be.

Here is an example:
For LF MAPPRPL6, the DDS has:
JFILE(VOENTITY MAPPRP)
JOIN(VOENTITY MAPPRP)
JFLD(VID MID)
Pertinent values from DSPDBR outfile:
WHRFI WHREFI WHJDIL WHJREF
-------------------------------------------------------
MAPPRP MAPPRPL6 0 2
VOENTITY MAPPRPL6 0 1

We're on 7.4, current on PTFs.
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