What is the difference between the wording of a special circumstance provision in the California Penal Code and the wording in section 189 of the Penal Code?

In Jones v. Superior Court (1981) 123 Cal.App.3d 160, 176 Cal.Rptr. 430, this court was confronted with another difference between the wording of a special circumstance provision and the wording [129 Cal.App.3d 1011] of Penal Code section 189. There, the phrase in section 189 provided that killing "in perpetration of" certain felonies was first degree murder and a body of case law had developed defining the "in perpetration of" phrase as including a period of flight to temporary safety. The special circumstance provided in part for the death penalty for one whose murder was committed while he was "engaged in" the commission of certain felonies. We concluded that the choice of wording was important and that to give the same interpretation of the terms "while engaged in" and "in perpetration of"

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