TargetScanHuman 7 and TargetScanMouse 7 display non-canonical sites, which are sites of interaction between a mRNA and a miRNA that do not involve the canonical pairing in the seed region (positions 2 - 7) of the miRNA.

Non-canonical sites are of two types: 3' compensatory and centered.

A 3' compensatory site is one in which strong 3' pairing (consequential miRNA-target complementarity outside the seed region) compensates for an imperfect seed match (Friedman et al., 2009).

A centered site is one that lacks perfect seed pairing and 3'-compensatory pairing but instead has 11-12 contiguous Watson-Crick pairs to miRNA positions 4-15. These are identified only in the reference species and therefore include no information about conservation. The context++ score is not calculated for these sites.