def _update_channels(nodes, root_pos_channels, rot_channels):
    """ Add information about channels in root position and joint rotations to nodes.
    
    :param nodes: Dictionary with skeleton hierarchy to update.
    :param root_pos_channels: Which position channels the root has.
    :type root_pos_channels: list
    :param rot_channels: Dictionary with mapping of joint name to list of its rotation channels.
    :type rot_channels: dict
    """
    for node, properties in nodes.items():
        if not properties['children']:
            continue
        if not properties['parent']:
            properties['channels'] = root_pos_channels + rot_channels[node]
        else:
            properties['channels'] = rot_channels[node]
