Or a DOMFS in /dom that's organized in the same hierarchy as the browser DOM. For example, to write a whole page:

    echo "...." > /dom

Update the <title> tag:

    echo "TITLE" > /dom/html/head/title

Change the charset:

    echo "EBCDIC" > /dom/html/head/meta[1].charset // second <meta> tag
    echo "EBCDIC" > /dom/html/head/1.charset       // second child of <head>

Even go full XPath and replace a tag's inner HTML:

    echo "<div>abc</div>" > /dom/[@id='myID']

This is a horrible idea...