import re


def is_possible_roman_numeral(string):
    """
    True if string is a possible Roman Numeral, False otherwise.
    Checks if only a combination of the following characters exist: IVXLCDM (upper case)
    Does not verify if it is a valid Roman Numeral.

    PARAMETERS:
        string : str

    RETURNS: bool
    """
    if 0 < len(string) <= 14:  # Longest Roman numeral (2888) has 14 characters
        # Matches strings that consist of IVXLCDM characters starting at index 0
        # If this happens, returns True if the whole string was matched, False otherwise
        match = re.match("[IVXLCDM]+", string)
        if match:
            return len(match.group()) == len(string)
    
    return False