Compare outlier detection methods with the OutliersO3 package

There are many different methods for identifying outliers and a lot of them are available in R. But are outliers a matter of opinion? Do all methods give the same results? Articles on outlier methods use a mixture of theory and practice. Theory is all very well, but outliers are outliers because they don't follow theory. Practice involves testing methods on data, sometimes with data simulated based on theory, better with real' datasets.