code: private String replacePosixClasses(String input) {
          return input
              .replace(":alnum:", "\\p{Alnum}")
              .replace(":alpha:", "\\p{L}")
              .replace(":ascii:", "\\p{ASCII}")
              .replace(":digit:", "\\p{Digit}")
              .replace(":xdigit:", "\\p{XDigit}");
      }
docs: Replace any specified POSIX character classes with the Java equivalent.
  
  @param input
  @return a Java regex