DSL EXPRESSION:
begin{unset $x}

AST:
"block" [tt:block] [nt:StatementBlock]
    "begin" [tt:kw_begin] [nt:BeginBlock]
        "block" [tt:block] [nt:StatementBlockInBraces]
            "block" [tt:block] [nt:StatementBlock]
                "unset" [tt:kw_unset] [nt:Unset]
                    "$x" [tt:field_name] [nt:DirectFieldValue]

