Boolean isLocalOverridable(String localName, DimensionBinding binding) {
        if (localLookup(localName, binding) == null) return null; // Not set
        if ( ! binding.isNull() && getVariants() != null) {
            Boolean variantIsOverriable = getVariants().isOverridable(localName, binding.getValues());
            if (variantIsOverriable != null)
                return variantIsOverriable;
        }
        Boolean isLocalInstanceOverridable = isLocalInstanceOverridable(localName);
        if (isLocalInstanceOverridable != null)
            return isLocalInstanceOverridable;
        if (type != null) return type.isOverridable(localName);
        return true;
    }
Returns true if this value is definitely overridable in this (set and not unoverridable),
false if it is declared unoverridable (in instance or type), and null if this profile has no
opinion on the matter because the value is not set in this.
container-search/src/main/java/com/yahoo/search/query/profile/QueryProfile.java