What is the test for establishing that an act committed in a territorial jurisdiction must be a necessary element of the crime?

'The argument that the act committed in a territorial jurisdiction must be one which involves a necessary element of the crime was long ago rejected in People v. Megladdery . . . where the court said that such an interpretation 'would completely disregard the phrase 'or the acts or effects thereof constituting or requisite to the consummation of the offense' contained in . . . section (781 of the Penal Code). Obviously, the phrase, 'or requisite to the consummation of the offense', means requisite to the completion of the offense--to the achievement of the unlawful purpose--to the ends of the unlawful enterprise. By the use of the word 'consummation' the legislature drew a distinction between an act or an effect thereof which is essential to the commission of an offense, and an act or effect thereof which, although unessential to the commission of the offense, is requisite to the completion of the offense--that is, to the achievement of the unlawful purpose of the person committing the offense. '' (Supra. 36 Cal.App.3d at p. 268, 111 Cal.Rptr. at p. 382.)