from typing import Iterable


def _value_to_triplet(source: str, start: str, end: str) -> Iterable[str]:
    """Extract the first tag value from a string, splitting the source string into the parts before and after the tag.

    :param source: String to process
    :param start: String that marks the start of a tag
    :param end: String that marks the end of a tag
    :return: Split string values
    """
    prefix, _value = source.split(start, 1)

    value, suffix = _value.split(end, 1)

    return prefix, value, suffix