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<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <body>
        <referenceBlock name="top.links">
            <block class="Your_NamespaceYour_ModulenameBlockLink" name="custom-link" after="my-account-link"/>
        </referenceBlock>
    </body>
</page>

namespace Your_NamespaceYour_ModulenameBlock;
/**
 * Class Link
 *
 * @SuppressWarnings(PHPMD.DepthOfInheritance)
 */
class Link extends MagentoFrameworkViewElementHtmlLink
{
    /**
     * Template name
     *
     * @var string
     */
    protected $_template = 'Your_Namespace_Your_Modulename::link.phtml';

    /**
     * @param MagentoFrameworkViewElementTemplateContext $context
     * @param array $data
     */
    public function __construct(
        MagentoFrameworkViewElementTemplateContext $context,
        array $data = []
    ) {
        parent::__construct($context, $data);
    }

    /**
     * @return string
     */
    public function getHref()
    {
        return $this->getUrl('custom/controller/action');
    }

    /**
     * @return MagentoFrameworkPhrase
     */
    public function getLabel()
    {
        return __('Your custom link');
    }
}

<li class="link custom">
    <a <?php /* @escapeNotVerified */ echo $block->getLinkAttributes() ?>><?php echo $block->escapeHtml($block->getLabel()) ?></a>
</li>