syntax_data: {"ast_node_type":"other","tokens":[{"end":73,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// the bound variables. Note: the (old or new) value itself does not
context_before:     /// current `Binder`. This should not be used if the new value *changes*
context_after:     /// necessarily need to *name* all the bound variables.