Evidence - Collateral Fact Rule
R v Sanderson (Ont CA, 2017)
Here the Court of Appeal cites the collateral fact rule as follows:
 Watt’s Manual of Criminal Evidence (Toronto: Carswell, Thomson Canada Limited, 2002), describes the rule as follows at para. 22.03, p. 265:
The collateral facts rule prohibits the introduction of evidence for the sole purpose of contradicting a witness’ testimony concerning a collateral fact. The rule seeks to avoid confusion and proliferation of issues, wasting of time and introduction of evidence of negligible assistance to the trier of fact in determining the real issues of the case. It endeavours to ensure that the sideshow does not take over the circus. In general, matters that relate wholly and exclusively to the credibility of a non-accused witness are collateral, hence beyond the reach of contradictory evidence.