This is the template used by the third counter/state example.
The odd curly-brace-percent things are non-literal. Double
curly braces substitute variable values, and the others are
a peculiar conditional language.
<html>
<head>
<meta charset="utf-8">
<title>Flask Sessions</title>
<link rel="stylesheet" href="/static/genstyle.css" type="text/css">
<style>
p, form * { text-align: center; }
</style>
</head>
<body>
<h1>Hello, Flask 3</h1>
<p>This script passes state using a Flask session.</p>
<form method="post">
<p>The current count is {{count}}.
You are {% if loggedin is false %}not {% endif %}logged in.</p>
<div><input type="submit"
{% if loggedin is true %}
name="LOGOUT" value="LOGOUT">
{% else %}
name="LOGIN" value="LOGIN">
{% endif %}
<input type="submit" name="next" value="next"></div>
</form>
</body>
</html>