d3_bind_enter_exit.js

d3.selectAll("div") // Returns selection.
  .data(someData)    // Bind each element in the selection to each element in `someData` array.
  .enter()           // The `enter` function defines what to do with the extra data not represented as a `div`.
  .append("div")     // In this case, you append a new div for every data that is not represented by a `div`.
  .html("Wow")       // with the html "Wow",
  .append("span")    // followed by a span,
  .html("More Wow")  // with more html.
  .style("font-weight", "900");  // Applies style to the very last result, which in this case, is the html "More Wow".