The core/meta.php can be used to add any <meta> tags required in your theme.

The theme engine loads the core/meta.php file in your theme directory and expects to find the theme_page_meta_tags hook defined. Your hook should return any <meta> tags that you require.

The following returns the old 4.01 transitional doctype.

function theme_page_meta_tags()
{
    return "
       <!-- Meta tags -->
       <meta charset='utf-8'>
       <meta name='viewport' content='width=device-width, initial-scale=1.0'>
    ";
}

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