public Checker tryCreate(String pattern) {
      Matcher matcher = BEGIN_PATTERN.matcher(pattern);
      if (matcher.matches()) {
        return new BeginChecker(matcher.group(1));
      }
      return null;
    }
Accepts simple REGEXP patterns like "abc.*" and creates corresponding checkers.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/FilterStringColRegExpStringScalar.java