nl_tokens: Used for preventing the next write () call on TransformStreamSink until there is no longer backpressure .
pl_tokens: function TransformStreamReadableReadyPromise ( transformStream ) { assert ( transformStream . _backpressureChangePromise !== undefined , '_backpressureChangePromise should have been initialized' ) ; if ( transformStream . _backpressure === false ) { return Promise . resolve ( ) ; } assert ( transformStream . _backpressure === <mask> , '_backpressure should have been initialized' ) ; return transformStream . _backpressureChangePromise ; }