cmsfn.search has been deprecated (as of M 5.4) in favor of
searchfn.searchContent

This seems to replace a fully fledged queryString search with keyword search:

[1] cmsfn.search eventually calls QueryUtil.search, which accepts a real SQL-ish statement: Query query = manager.createQuery(statement, language);

[2] searchfn.searchContent eventually calls Query query = jcrQueryManager.createQuery(String.format(SEARCH_QUERY_PATTERN ...)) where SEARCH_QUERY_PATTERN = "SELECT rep:excerpt() from %s WHERE jcr:path like '%s/%%' AND contains(., '%s') ORDER BY jcr:score DESC";