How do corrections in Cost Reports relate to the corrected lines?

Hello. I'm looking for some clarification on how the corrections described in the Cost Reports documentation actually work.

Cost reports can contain corrections. Corrections are added as new rows to the report, with the lineItem/iscorrection column set and the referenceNo value of the corrected line populated in the lineItem/backReference column.

Are these corrections intended to entirely replace the back-referenced line items (as I suspect), or are their values intended to be added to those of the corrected item? (I haven't seen any corrections in our cost reports such that I could try and confirm for myself.)

Thanks in advance for any input on this.