This is not something currently specified in the mozilla coding style but I believe it would make things much more readable with no confusion possible. Currently, clang-format attempt to always fill as much as possible within 80 columns. example it will format the line as: return (aDecoder.HasPromise() || aDecoder.mTimeThreshold.isSome()) && !aDecoder.HasPendingDrain() && !aDecoder.HasFatalError() && !aDecoder.mDemuxRequest.Exists() && !aDecoder.mOutput.Length() && !aDecoder.HasInternalSeekPending() && !aDecoder.mDecodeRequest.Exists(); ignore the fact that the && operator is incorrectly placed at the end of the line (see bug 1338105) To be spec compliant it should be written: return (aDecoder.HasPromise() || aDecoder.mTimeThreshold.isSome()) && !aDecoder.HasPendingDrain() && !aDecoder.HasFatalError() && !aDecoder.mDemuxRequest.Exists() && !aDecoder.mOutput.Length() && !aDecoder.HasInternalSeekPending() && !aDecoder.mDecodeRequest.Exists(); But this is difficult to read, because it has placed more than one operation on a line as it fitted within 80 columns. and it would be more readable written as: return (aDecoder.HasPromise() || aDecoder.mTimeThreshold.isSome()) && !aDecoder.HasPendingDrain() && !aDecoder.HasFatalError() && !aDecoder.mDemuxRequest.Exists() && !aDecoder.mOutput.Length() && !aDecoder.HasInternalSeekPending() && !aDecoder.mDecodeRequest.Exists(); The first: (aDecoder.HasPromise() || aDecoder.mTimeThreshold.isSome()) can be written on a single line, because it is one logical statement, not involving the other operators and has higher priority. same with: if ((decoder.mWaitingForData && (!decoder.mTimeThreshold || decoder.mTimeThreshold.ref().mWaiting)) || (decoder.mWaitingForKey && decoder.mDecodeRequest.Exists())) { } the above is correct and preferred.