Elsewhere insertion realizes at each grade the exponent of the applicable rule of greatest
threshold, the most specific, the first listed on ties, and none where no rule applies.
- realize v = v.realize SpanRule.threshold
Used by realize_realizes, realize_eq_of_threshold_le, pattern_toDecomposition
Used in Morphology/Exponence/Containment/Contiguity, Bobaljik2012, Graf2019, SmithMoskalEtAl2019