Jerome Cukier hat ein Tutorial zu D3 erstellt und ich habe alles mitgemacht, denn er hat mich gleich zu Beginn erwischt.
copy, paste!
I have learned d3 from deciphering script examples and in the earliest ones one ubiquitous construct was this sequence : select / selectAll / data / enter / append.
It does the work, so like everyone else I’ve copied it and reused very often. It happens to be the most proper way of adding new elements in most cases, but the point is, while learning d3, I (and many people before and after me) have copy/pasted it without understanding it deeply.