syntax_data: {"ast_node_type":"other","tokens":[{"end":71,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// Parse an optional language identifier, e.g. `en-US` or `zh-CN`.
context_after:     pub(crate) fn parse_opt_langid(slot: &mut Option<LanguageIdentifier>, v: Option<&str>) -> bool {