Looks like you're setting the <iframe>'s contents with a data uri in the src att...

Looks like you're setting the <iframe>'s contents with a data uri in the src attribute, you save some characters if you use the HTML5 srcdoc attribute:

    <x id=e><script>for(i=4;i--;)e.innerHTML+=(i?'<textarea':'<iframe')+' id=t'+i+' style=width:49%;height:48% oninput=\'t0.srcdoc=t3[v="value"]+"<script>"+t1[v]+"<\/script><style>"+t2[v]\'>'</script>

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/if...

http://www.whatwg.org/specs/web-apps/current-work/multipage/...