What is storedvars in selenium ide?

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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head profile="http://selenium-ide.openqa.org/profiles/test-case">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<link rel="selenium.base" href="http://demo.opensourcecms.com/" />
<title>storedVars</title>
</head>
<body>
<table cellpadding="1" cellspacing="1" border="1">
<thead>
<tr><td rowspan="1" colspan="3">storedVars</td></tr>
</thead><tbody>
<tr>
    <td>store</td>
    <td>10</td>
    <td>var1</td>
</tr>
<tr>
    <td>echo</td>
    <td>${var1}</td>
    <td></td>
</tr>
<tr>
    <td>echo</td>
    <td>javascript{storedVars['var1']}</td>
    <td></td>
</tr>
<tr>
    <td>store</td>
    <td>${var1}</td>
    <td>var2</td>
</tr>
<tr>
    <td>echo</td>
    <td>javascript{storedVars['var1']}</td>
    <td></td>
</tr>
<tr>
    <td>echo</td>
    <td>${var2}</td>
    <td></td>
</tr>
<tr>
    <td>store</td>
    <td>javascript{storedVars['var1']}</td>
    <td>var3</td>
</tr>
<tr>
    <td>echo</td>
    <td>value of ${var3}</td>
    <td></td>
</tr>
<tr>
    <td>storeEval</td>
    <td>storedVars['var2']</td>
    <td>var4</td>
</tr>
<tr>
    <td>echo</td>
    <td>${var4}</td>
    <td></td>
</tr>
<tr>
    <td>storeEval</td>
    <td>new Number(${var1}) + 10</td>
    <td>var5</td>
</tr>
<tr>
    <td>echo</td>
    <td>${var5}</td>
    <td></td>
</tr>
</tbody></table>
</body>
</html>