What is the test for establishing that a residential district is a commercial district?

Bortz v. Troth, 359 Pa. 326, 59 A.2d 93, 97: 'What appellee in effect suggests, and what the court en banc bas done, is to declare a neighborhood to be in a transitional stage because not far away there are commercial enterprises, the operation of which would be prevented in an exclusively residential district. To establish that principle as one of law will negative the existence of lines of demaraction dividing commercial, residential and exclusively residential districts. Commercial areas would be moved forward without restraint, except that equitable relief might be afforded if the given business were shown to constitute a nuisance in fact. Fringe areas would advance so that block after block would steadily succumb to inroads of industrial enterprises. * * * The error of the majority of the court en banc was overemphasis upon the proximity of existing business enterprises and failure to recognize the fact that no inroads had

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