I've just tracked down a nasty little problem porting some code to Pharo. As a result, I have added to the comments in my own versions of these methods. beginsWith: aSequence "Answer true if aSequence is a prefix of the receiver. This makes sense for all sequences. There is a compatibility issue concerning 'abc' beginsWith: '' + VisualWorks, Dolphin, astc, GNU ST (where the method is called #startsWith:) and VisualAge (where the method is called #wbBeginsWith:) agree than EVERY sequence begins with an empty prefix. - Squeak and Pharo agree that NO sequence begins with an empty sequence. # ST/X chooses compatibility with Squeak, heaving a big unhappy sigh, and adds #startsWith: to have something sensible to use. Now ST/X *thinks* it is compatible with VW, though it isn't, so I wonder if this was a bug that VW fixed and Squeak didn't? astc goes with the majority here. This is also compatible with Haskell, ML, and with StartsWith in C# and startsWith in Java." ^self beginsWith: aSequence ignoringCase: false endsWith: aSequence "Answer true if aSequence is a suffix of the receiver. This makes sense for all sequences. There is a compatibility issue concerning 'abc' endsWith: ''. + VisualWorks, Dolphin, astc, GNU ST, and VisualAge (where the method is called #wbEndsWith:) agree that EVERY sequence ends with an empty suffix. - Squeak and Pharo agree that NO sequence ends with an empty suffix. # ST/X chooses compatibility with the majority, apparently unaware that this makes #beginsWith: and #endsWith: inconsistent. astc goes with the majority here. This is also compatible with Haskell, ML, C#, and Java." ^self endsWith: aSequence ignoringCase: false Does anyone have any idea - why Squeak and Pharo are the odd ones out? - why anyone thought making #beginsWith: and #endsWith:, um, "quirky" was a good idea (it's pretty standard in books on the theory of strings to define "x is a prefix of y iff there is a z such that y = x concatenated with z") I was about to try to file a bug report for the first time, then realised that maybe other people don't think this IS a bug.