syntax_data: {"ast_node_type":"other","tokens":[{"end":65,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // void register_callback(void (*fn)(void *), void *arg);
context_before:         // cleanup handlers (in C, this would be something along the lines of:
context_after:         // (see src/libstd/sys/pal/unix/fast_thread_local.rs) that is currently