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Our names are personal things that people attach great value to, so in general we should try to accommodate a person's full name. However at the same time, a persons name (especially in an app) is read by other people more often than it is read by themselves, and is primarily there to identify them to someone else. So there is a solid argument for a name length limit.
The question then becomes, what a sane length limit is.
The UK Government uses a limit of 70 characters for a full name field in their internal systems, but it seems to me that 70 characters is somewhat excessive if usability is the prime criterion.
Does anyone know of any studies on limiting a users name length (the name that is displayed, not their username) and the UX implications? Feedback from experience and UX testing of this would also be good.
Please note that I am not asking how to display a long name or about technical issues in implementing long names. For that there are already good answers. This is solely about the UX considerations in choosing a name length limit.