def _determine_selected_stencil(stencil_set, stencil_definition):
    """Determine appropriate stencil name for stencil definition.

    Given a fastfood.json stencil definition with a stencil set, figure out
    what the name of the stencil within the set should be, or use the default
    """
    if 'stencil' not in stencil_definition:
        selected_stencil_name = stencil_set.manifest.get('default_stencil')
    else:
        selected_stencil_name = stencil_definition.get('stencil')
    if not selected_stencil_name:
        raise ValueError(
            'No stencil name, within stencil set %s, specified.' %
            stencil_definition['name'])
    return selected_stencil_name
