code: private static Map<String, Integer> appendDisplayNames(final Calendar cal, final Locale locale, final int field, final StringBuilder regex) {
  		final Map<String, Integer> values = new HashMap<>();
  
  		final Map<String, Integer> displayNames = cal.getDisplayNames(field, Calendar.ALL_STYLES, locale);
  		final TreeSet<String> sorted = new TreeSet<>(LONGER_FIRST_LOWERCASE);
  		for (final Map.Entry<String, Integer> displayName : displayNames.entrySet()) {
  			final String key = displayName.getKey().toLowerCase(locale);
  			if (sorted.add(key)) {
  				values.put(key, displayName.getValue());
  			}
  		}
  		for (final String symbol : sorted) {
  			simpleQuote(regex, symbol).append('|');
  		}
  		return values;
  	}
docs: Get the short and long values displayed for a field
  
  @param cal The calendar to obtain the short and long values
  @param locale The locale of display names
  @param field The field of interest
  @param regex The regular expression to build
  @return The map of string display names to field values