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First, although obvious in retrospect, users do not always use the interface as originally intended. We observed this during paper prototyping, as users repeatedly clicked on a class name whenever we asked them to add an assignment. We decided to embrace it and this was implemented in our final design.
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.