A site wrote their report in the DPM MRI.PAT and using the detail segment mri.patient.file. They wanted to print the patient's merged from unit number.  We recommended the following:

xx.merged.from
DAT=FREE
JFY=L
LEN=10
VAL=IF{""^FND^merged.number,
VAL=DO{@Next(merged.number) @MRI.PAT.px.unit.number[@merged.urn,
VAL=@.mri.pfx]^FND},FND}