@ ProgramNode (location: (1,0)-(1,15))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,15))
    └── body: (length: 1)
        └── @ AliasGlobalVariableNode (location: (1,0)-(1,15))
            ├── new_name:
            │   @ GlobalVariableReadNode (location: (1,6)-(1,12))
            │   └── name: :$MATCH
            ├── old_name:
            │   @ BackReferenceReadNode (location: (1,13)-(1,15))
            │   └── name: :$&
            └── keyword_loc: (1,0)-(1,5) = "alias"