private List<ExpressionNode> createTokenSequence(ReferenceNode feature, ExpressionNode cls, ExpressionNode sep, int fromArg) {
        List<ExpressionNode> sequence = new ArrayList<>();
        sequence.add(cls);
        for (int i = fromArg; i < feature.getArguments().size(); ++i) {
            sequence.add(feature.getArguments().expressions().get(i));
            sequence.add(sep);
        }
        return sequence;
    }
Transforms a feature of the form

    tokenAttentionMask(128, a, b, ...)

to an expression that generates a tensor that has values 1 for all
arguments (including CLS and SEP tokens) and 0 for the rest of the
sequence.

Concretely, transforms to a tensor generation expression:

    tensor(d0[1],d1[128])(if(d1 < 1 + length_a + 1 + length_b + 1 + ..., 1, 0))
config-model/src/main/java/com/yahoo/schema/expressiontransforms/TokenTransformer.java