It seems to me that just about any important product or system is worth engineering. Before you start building it, you'd better understand the problem, design a workable solution, implement it in a solid way, and test it thoroughly. You should probably also control changes to it as you work and have some mechanism for ensuring the end result's quality. Many Web developers don't argue with this; they just think their world is really different and that conventional software engineering approaches simply don't apply.
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