/**
* Returns a substring from a string.
*
* As a special case, the method returns an empty string if the starting position is equal to the string's length
* or if the substring's length, if specified, is `0`.
*
* @param int $startPos The position of the substring's first character.
* @param int $length **OPTIONAL. Default is** *as many characters as the starting character is followed by*. The
* length of the substring.
*
* @return CUStringObject The substring.
*/
public function substr($startPos, $length = null)
{
return CUString::substr($this, $startPos, $length);
}