src/etc/adminhtml/system.xml
<?xml version="1.0"?>
<!--
* Licensed under Academic Free License ("AFL") v. 3.0
* See LICENSE.txt or https://opensource.org/licenses/afl-3.0
*
* @category Siment_HttpHeaderThemeSwitch
* @copyright (c) 2017 Simen Thorsrud
* @author Simen Thorsrud <simen.thorsrud@gmail.com>
-->
<config
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
<system>
<section id="design">
<group
id="http_header_theme_switch"
translate="label"
type="text"
sortOrder="25"
showInDefault="1"
showInWebsite="1"
showInStore="1">
<label>HTTP Header Theme Switch</label>
<field
id="siment_http_header_theme_switch_http_header"
translate="label comment"
type="text"
sortOrder="40"
showInDefault="1"
showInWebsite="1"
showInStore="1"
canRestore="1">
<label>HTTP Header</label>
<comment><![CDATA[HTTP header which will be matched for theme exceptions in
addition to the standard header "User-Agent".<br /></br />You define the matching rules under <b>Content</b>
-> (Design) <b>Configuration</b> -> (Select a theme) <b>Edit</b> -> <b>User Agent Rules</b>]]></comment>
<config_path>siment_http_header_theme_switch/general/http_header</config_path>
</field>
</group>
</section>
</system>
</config>