If there's one, remove the YAML front-matter from the source

def remove_yaml_frontmatter(source, return_frontmatter=False):
    """If there's one, remove the YAML front-matter from the source
    """
    if source.startswith("---\n"):
        frontmatter_end = source.find("\n---\n", 4)
        if frontmatter_end == -1:
            frontmatter = source
            source = ""
        else:
            frontmatter = source[0:frontmatter_end]
            source = source[frontmatter_end + 5:]
        if return_frontmatter:
            return (source, frontmatter)
        return source
    if return_frontmatter:
        return (source, None)
    return source