On Apr 8, 2014, at 17:32, John Laing <john.laing at gmail.com> wrote: > > That doesn't feel very eXtensible to me. > xts is quite obviously past tense. ;-) The list of allowable index classes is found in is.timeBased IIRC and the exclusion of integers is because there's no obvious way to have them play nice with other index classes. M