public Builder add(String dimension, String label) {
            Objects.requireNonNull(dimension, "dimension cannot be null");
            Objects.requireNonNull(label, "label cannot be null");
            int labelIndex = type.indexOfDimensionAsInt(dimension);
            if ( labelIndex < 0)
                throw new IllegalArgumentException(type + " does not contain dimension '" + dimension + "'");
            labels[labelIndex] = LabelCache.GLOBAL.getOrCreateLabel(label);
            return this;
        }
Adds a label in a dimension to this.

@return this for convenience
vespajlib/src/main/java/com/yahoo/tensor/TensorAddress.java