syntax_data: {"ast_node_type":"other","tokens":[{"end":51,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// - for `cfg(target_feature)`, check `in_cfg`
context_before:     /// - for `#[target_feature]`/`-Ctarget-feature`, check `allow_toggle()`
context_after:     pub fn requires_nightly(&self) -> Option<Symbol> {