how can i edit outerHtml element

[bag7dad]

i have this element

<div class="n">hello <a>world</a></div>

i just want to edit this outerHtml and add space between text and element so its be like this

<div class="n"> hello <a> world </a></div>

i read the Readme and didn't find any method for change outerHtml or innerHtml

like

$domx->getSimpleNode()->innertext = $article;