DSL EXPRESSION:
begin{@x=$y}

AST:
"block" [tt:block] [nt:StatementBlock]
    "begin" [tt:kw_begin] [nt:BeginBlock]
        "block" [tt:block] [nt:StatementBlockInBraces]
            "block" [tt:block] [nt:StatementBlock]
                "=" [tt:equals] [nt:Assignment]
                    "@x" [tt:oosvar_name] [nt:DirectOosvarValue]
                    "$y" [tt:field_name] [nt:DirectFieldValue]

