public boolean isRule(final String symbol) {
    return ((symbol != null) && (RULES.contains(symbol.toLowerCase(Locale.ENGLISH))));
  }
Determine if specified string is a known operator.

@param symbol string
@return true if string is a known operator
olv-core/src/main/java/pl/otros/logview/accept/query/org/apache/log4j/rule/RuleFactory.java