docs: private String convertWildcardExpressionToRegularExpression(final String pWildcardExpression) {
  
      if (pWildcardExpression == null) {
        if (mDebugging) {
          out.println(DebugUtil.getPrefixDebugMessage(this) + "wildcard expression is null - also returning null as regexp!");
        }
        return null;
      }
      StringBuilder regexpBuffer    = new StringBuilder();
      boolean      convertingError = false;
  
      for (int i = 0; i < pWildcardExpression.length(); i++) {
        if (convertingError) {
          return null;
        }
  
        // Free-range character '*'
        char stringMaskChar = pWildcardExpression.charAt(i);
  
        if (isFreeRangeCharacter(stringMaskChar)) {
          regexpBuffer.append("(([a-�A-�0-9]|.|_|-)*)");
        }
  
        // Free-pass character '?'
        else if (isFreePassCharacter(stringMaskChar)) {
          regexpBuffer.append("([a-�A_�0-9]|.|_|-)");
        }
  
        // Valid characters
        else if (isInAlphabet(stringMaskChar)) {
          regexpBuffer.append(stringMaskChar);
        }
  
        // Invalid character - aborting
        else {
          if (mDebugging) {
            out.println(DebugUtil.getPrefixDebugMessage(this)
                        + "one or more characters in string mask are not legal characters - returning null as regexp!");
          }
          convertingError = true;
        }
      }
      return regexpBuffer.toString();
    }