syntax_data: {"ast_node_type":"other","tokens":[{"end":81,"kind":"keyword","start":0,"text":"allow_features:"}]}
source_snippet:     allow_features: Option<Vec<String>> = (None, parse_opt_comma_list, [TRACKED],
context_before:     // tidy-alphabetical-start
context_after:         "only allow the listed language features to be enabled in code (comma separated)"),