def get_by_type_and_title(page, type_, title):
    """
    Find the child block of page of type `type_` and title `title`.
    Raises if it finds multiple matches. Returns None if not found.
    """
    results = []
    for block in page.children:
        if block.type == type_ and block.title == title:
            results.append(block)
    if not results:
        return None
    assert len(results) == 1, 'ERROR: found multiple matches'
    return results[0]