code: public static final Function<String,Boolean> isCalendar(final String pattern, final Locale locale) {
          return new IsCalendar(pattern, locale);
      }
docs: <p>
  Checks whether the target {@link String} represents a {@link Calendar} or not.
  If it returns true, {@link FnString#toCalendar(String, Locale)} can be called
  safely.
  </p>
  <p>
  Pattern format is that of <tt>java.text.SimpleDateFormat</tt>.
  </p>
  
  @param pattern the pattern to be used.
  @param locale the locale which will be used for parsing month names
  @return true if the target {@link String} represents a {@link Calendar},
  false otherwise