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Second, before adding UI niceties that may require deviating from conventional web applications, it is worth assessing their real need. In the time spent to implement live validation, it would be possible to implement several other features.
Third, it is worth mentioning that most problems identified during heuristic evaluation were actually implementation faults; this is an indication that most design problems were filtered out during earlier paper prototyping sessions - which is good, since as we have seen they tend to be much cheaper.