Magento 2’s Poorly Named Layout Argument Nodes

Magento 2 introduced a new node type to its Layout XML DSL — the <arguments/> and <argument/> node.

#File: vendor/magento/module-shipping/view/frontend/layout/sales_guest_view.xml
<referenceBlock name="sales.order.view">
    <block class="Magento\Shipping\Block\Tracking\Link" name="tracking-info-link" template="Magento_Shipping::tracking/link.phtml">
        <arguments>
            <argument name="label" xsi:type="string" translate="true">
                Track your order
            </argument>
        </arguments>
    </block>
</referenceBlock>

Like so much of Magento — the names of these new nodes hide their purpose from developers. All the <argument/> nodes do ensure a value will be set on the final block object. i.e. The above code will set a label property on the tracking-info-link block (instantiated from the PHP class Magento\Shipping\Block\Tracking\Link). This means you can access the property from your phtml template like this

$block->getLabel();
$block->getData('label');

You can see this in the Magento_Shipping::tracking/link.phtml template file.

#File: vendor/magento/module-shipping/view/frontend/templates/tracking/link.phtml
<span><?= /* @escapeNotVerified */ $block->getLabel() ?></span>   

Behind the scenes, this functionality is implemented by Magento looking for these argument nodes, and then passing additional information into the Block class when instantiating a Block object. That’s why these nodes are called <arguments/> and <argument/> — because the system designer was focused on the implementation details of the system instead of how end user programmers would use the system.