This as-simple-as-possible example tries to demonstrate Mike Bostock's pattern "Towards Reusable Charts" http://bost.ocks.org/mike/chart/ for d3 plugins that are composite shapes.
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8">
<title>really simple d3 plugin example</title>
</head>
<style>
body {
font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
width: 960px;
height: 500px;
position: relative;
}
</style>
<body>
<div id="chart">
</div>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script type="text/javascript" src="textblock.js"></script>
</body>
</html>
Modified http://d3js.org/d3.v3.min.js to a secure url
https://d3js.org/d3.v3.min.js