"""Constructs a hexadecimal version string from version components.

This function processes version components (major, minor, patch level, and serial) to generate a hexadecimal representation of the version. The patch level can include a level identifier (e.g., 'a', 'b', 'c', 'dev') and a serial number.

Args:
    matches (Dict[str, Union[int, str]]): A dictionary containing version components with keys 'MAJOR', 'MINOR', and 'PATCH'. 'MAJOR' and 'MINOR' are expected to be integers, while 'PATCH' is a string that may include a level identifier and serial number.

Returns:
    str: A hexadecimal string prefixed with '0x' representing the version. The format is '0xMMmmppLs', where:
        - MM: Major version (2 hex digits)
        - mm: Minor version (2 hex digits)
        - pp: Patch version (2 hex digits)
        - L: Level identifier (1 hex character, e.g., 'a' -> 'A', 'b' -> 'B')
        - s: Serial number (1 hex digit)

Raises:
    RuntimeError: If the 'PATCH' component is invalid or cannot be parsed.

Examples:
    >>> build_expected_version_hex({'MAJOR': 1, 'MINOR': 2, 'PATCH': '3'})
    '0x01020300'
    >>> build_expected_version_hex({'MAJOR': 4, 'MINOR': 5, 'PATCH': '6.a7'})
    '0x040506A7'
    >>> build_expected_version_hex({'MAJOR': 8, 'MINOR': 9, 'PATCH': '10.b11'})
    '0x08090ABB'
"""