mpe_derived used &dc_dttmtfmt in its where= but the guard only checked libds and
dclib, so an unset value turned the filter into 'lt tx_to' and the control-table
step failed with a syntax error a long way from the cause. It is now part of
the guard, named in the message.
The 7.19 migration took max(selectbox_rk) into a macro variable, which is
missing on an install whose MPE_SELECTBOX is still empty - %eval(&maxrk+1) then
fails. coalesce(max(selectbox_rk),0) makes the first row start at 1.
dc
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