Javascript question

How do you add some content in a specific place in Javascript at the user's bequest? I'm writing a sort of CSS designer with the idea that it shows the user what the style looks like by writing it to a file and then loading it (using PHP). The thing is I want it to actually be useful, so it needs to be able to have as many elements and properties as the user wants. I know that trick where you have an empty <div> and set its innerHTML member but that will leave me a set number, and I don't want to just stick billions and billions of <div> tags inside my code (its already messy enough).

tl; dr how do I dynamically instert code into a webpage at a set position but allowing an arbitrary number of insertions?

>>17
I have looked at the error console, no errors were being reported.

function add_property()
{
    alert("Add property");
    var div = document.createElement("div");
    div.innerHTML = document.getElementById("ee2e7a91").innerHTML;
    document.body.appendChild(div);
}
The alert is displayed but nothing else happens (the page source when viewed from Firefox stays the same (yes, I re-opened it, I know it doesn't refresh automatically)).