syntax_data: {"ast_node_type":"other","tokens":[{"end":13,"kind":"keyword","start":0,"text":"Unstable("}]}
source_snippet:     Unstable(
context_before:     /// nightly and using it in `#[target_feature]` requires enabling the given nightly feature.
context_after:         /// This must be a *language* feature, or else rustc will ICE when reporting a missing