private ExpressionNode transformTokenInputIds(ReferenceNode feature, RankProfileTransformContext context) {
        return transformTokenInputIds(feature, context, CLS, SEP, 1);
    }
Transforms a feature of the form

    tokenInputIds(128, a, b, ...)

to an expression that concatenates the arguments a, b, ... using the
special Transformers sequences of CLS and SEP, up to length 128, so
that the sequence becomes

    CLS + a + SEP + b + SEP + 0's

Concretely, transforms to a tensor generation expression:

    tensor(d0[1],d1[128])(
        if (d1 < 1,
            101,
        if (d1 < 1 + length_a,
            a{d0:(d1 - (1)},
        if (d1 < 1 + length_a + 1,
            102,
        if (d1 < 1 + length_a + 1 + length_b,
            b{d0:(d1 - (1 + length_a + 1))},
        if (d1 < 1 + length_a + 1 + length_b + 1,
            102,
            0.0
        ))))))

Functions calculating lengths of arguments are added to the rank profile.
config-model/src/main/java/com/yahoo/schema/expressiontransforms/TokenTransformer.java