What is the test for setting aside a parent's custodial claim against a parent who cannot raise their child?

British Columbia, Canada

The following excerpt is from Chera v. Chera, 2008 BCCA 374 (CanLII):

The trial judge referred to the test outlined in A.L. v. D.K., 2000 BCCA 455, 190 D.L.R. (4th) 108, where Newbury J.A., relying on the earlier comments in King v. Low, 1985 CanLII 59 (SCC), [1985] 1 S.C.R. 87, concluded that custodial claims by one or both parents should not be lightly set aside in favour of custodial claims by third parties (e.g., grandparents, adoptive parents) unless there is a clear reason why one or both parents cannot raise their child.

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