{"ast_node_type":"other","tokens":[{"end":62,"kind":"keyword","start":0,"text":"($(<$K:ident:"}]}
    ($(<$K:ident: $Kb:ident>)? |&mut $self:ident: $self_ty:ty,
macro_rules! impl_walkable {
      $vis:ident: &mut $vis_ty:ident| $block:block) => {