syntax_data: {"ast_node_type":"other","tokens":[{"end":21,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     ///     mod foo {
context_before:     /// macro m($i:ident) {
context_after:     ///         pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.