How has the harmless error rule been applied to exclude evidence and testimony in a drug case?

While it would not be useful in this case to enlarge on the scope of harmless error, it is enough to elaborate on this instance of the rule's application. (For a restatement of the harmless error rule see People v. Crimmins, 36 N.Y.2d 230, 367 N.Y.S.2d 213, 326 N.E.2d 787.) The evidence and testimony excluded did not relate directly to any fact or element of the crimes charged involving drug transactions. The excluded evidence became relevant only because the prosecution in cross-examination of defendant on a concededly collateral matter educed partial admissions of a collateral fact, that is,

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