how to find words within a range in a TreeSet<String> using regular expressions (java)

while (it.hasNext()) {
  System.out.println(it.next());
}

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String pattern = "[^m-z]";

"^[m-z]"

wordSet.tailSet("m", true);

wordSet.subSet("b", true, "z", false);

while (it.hasNext()) {
    String element = it.next();
    if (element.toLowerCase().matches("^[m-z].*")) {
        System.out.println(element);
    }
}

while (it.hasNext()) {
    String element = (String) it.next();
    char c = element.charAt(0);
    if (c >= 'm' && c <= 'z') {
        System.out.println(element);
    }
}