468060 (122) [Avatar] Offline
p. 81 it says "We add child elements to the .append() function, and we need to declare it as a variable tweetG. This allows tweetG to sand in for d3.select("svg").selectAll("g"). so we don't have to retype it throughout this example.

.append is a method call of d3. You can't 'add child elements' to a method call.

You are not 'declaring' either append() or d3.select("svg").selectAll("g") as a variable. You are defining the variable tweetG as the return from d3.select() and a series of other chained method calls (as shown in the code listing).
elijah.meeks (127) [Avatar] Offline
You're right, that's a sloppy way for me to express that, I've changed it for the final edition.