syntax_data: {"ast_node_type":"other","tokens":[{"end":63,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // all to join up at a single shared pre-binding block.
context_before:         // so that they aren't visible after match tree lowering, and wire them
context_after:         // (Note that the subcandidates have already had their part of the match