public static Set<TokenType> getKeywordsRequiredBefore(final TokenType tokenType) {
        return getKeywordSet(tokenType, KEYWORDS_REQUIRED_BEFORE);
    }
@return A set of {@link TokenType}s that MUST appear in the query before tokenType.
stroom-query/stroom-query-api/src/main/java/stroom/query/api/token/TokenType.java