Simple but crucial user interfaces in the World Wide Web : introducing 20 guidelines for usable web form design, user interfaces

The World Wide Web contains a wide range of different web form design solutions for similar interface aspects and problems. Exemplarily, Figure 1 shows four different ways of implementing and communicating format restrictions to users. It can be seen, that even website developers of major companies choose very different ways to solve the same problems. This raises several important questions: Are these solutions equivalent or are there ways that lead to superior web forms in terms of an enhanced usability? Would it not be advantageous to use similar solutions for similar problems, so that predictability for users can be increased? Are there different solutions that may be used depending on the developer intentions?