OPEIntegrateDelta[expr, x, m] introduces the \delta(1-x) (DeltaFunction[1-x]).
The Mathematica Integrate function is called and each integration (from 0 to 1) is recorded for reference (and bug-checking) in the list $MIntegrate.
Notice that the dimension specified by the option should also be the dimension used in expr. It is replaced in OPEIntegrateDelta by (4+Epsilon).