Content for header
From Shopify Wiki
This tag is used without any parameters and must always be included somewhere in the <head>..</head> section of theme.liquid.
Several vital code snippets are inserted by Shopify in its place. For example google analytics tracking, shopify dashboard stats tracking and similar services are integrated into the custom templates this way.
<html>
<head>
<title>My Shop!</title>
...
{{ content_for_header }}
</head>
<body>
....
</body>
</html>
