[dllthomas]

I really don't like either "the rule of 3" or WET because I think they take the focus off the part of DRY that matters. It shouldn't be about syntactic repetition, but (as originally stated) about repetition of pieces of knowledge.

The focus on syntax misleads in two ways. First, it sometimes motivates consolidation of things that are merely coincidentally syntactically similar (pushing back on this is most of where WET and Ro3 are useful, when they are), which makes it harder to update the code when one "piece of knowledge" needs updating but not the other(s). If you have 10 things that all happen to be identical today, but any of them might change independently in any direction, combining them isn't "more DRY".

Second, the same piece of knowledge may be repeated in different syntax. If your setup means you have to say "there's a button here" one way in HTML, another way in JS, and another way in CSS, then combining those would be "more DRY" even though no syntax repeats. This isn't to say that combining those (say through code generation?) would necessarily be better - DRY is a guideline to be balanced against other guidelines; but I do assert that it is a more useful guideline when we think in terms of duplicated knowledge than in terms of duplicated syntax.