def merge_text_meta(left_text, right_text, overwrite=False):
    """
    Merge known text keys from right to left, add unknown text_keys.
    """
    if overwrite:
        left_text.update(right_text)
    else:
        for text_key in right_text.keys():
            if not text_key in left_text:
                left_text[text_key] = right_text[text_key]

    return left_text