• The D3 Data Operator binds data to a DOM element's __data__ property
• This "data" persists after the data operation, so that it is available on re-selection
• The D3 Update Selection represents the DOM elements from the prior selection that were successfully bound to the specified data elements (remember - unless a key-function is specified, it's done left to right)
• The D3 Exit Selection represents the DOM elements from the prior selection that were not successfully bound to the specified data elements
• The D3 Enter Selection represents the data for which no corresponding existing DOM element was found
• The D3 Enter Selection returns a selection of placeholder JavaScript objects
• The D3 Enter Selection only allows the .append, .insert, and .select operators at this time
• The D3 Enter Selection is only defined on selections returned by the D3 Data Operator

D3 Video Tutorial Lesson:

• D3 Data Operator