The concern would be that people tend to test against implementation not specification, so if they happen to test with a server that accepts 1MB files, and another is much stricter, problems could ensue. See the Content-Type header in HTTP as an example; in theory a client can indicate character set of a request body using a parameter on the Content-Type, however as early versions of IE didn't send the character set, many web applications were developed without taking this into account. By the time there was a push to use the character set parameter, it was generally considered that it would break too many implementations. This lead to this particularly terrible workaround: http://web.archive.org/web/20060427012511/http://ppewww.ph.gla.ac.uk/~flavell/charset/form-i18n.html