public FieldSet parse(DocumentTypeManager docMan, String fieldSet) {
        if (fieldSet.length() == 0) {
            throw new IllegalArgumentException("Illegal field set value \"\"");
        }

        if (fieldSet.startsWith("[")) {
            return parseSpecialValues(fieldSet);
        }

        StringTokenizer tokenizer = new StringTokenizer(fieldSet, ":");
        if (tokenizer.countTokens() != 2) {
            throw new IllegalArgumentException(
                    "The field set list must consist of a document type, " +
                    "then a colon (:), then a comma-separated list of field names");
        }

        String type = tokenizer.nextToken();
        String fields = tokenizer.nextToken();

        return parseFieldCollection(docMan, type, fields);
    }
TODO: Move to document and implement
document/src/main/java/com/yahoo/document/fieldset/FieldSetRepo.java