syntax_data: {"ast_node_type":"other","tokens":[{"end":125,"kind":"keyword","start":0,"text":"$reg:ident:"}]}
source_snippet:             $reg:ident: $class:ident $(, $extra_class:ident)* = [$reg_name:literal $(, $alias:literal)*] $(% $filter:ident)?,
context_before:         $(
context_after:         )*