syntax_data: {"ast_node_type":"other","tokens":[{"end":39,"kind":"keyword","start":0,"text":"|"}]}
source_snippet:             | (FnMut,   FnMut | FnOnce)
context_before:               (Fn, Fn | FnMut | FnOnce)
context_after:             | (FnOnce,          FnOnce) => true,