html - How do you nest a select inside of another select using javascript? -

html doesnt allow next:

<script>   function openwindow(){     document.getelementbyid("a").innerhtml = "<select><option>etc</option> </select>"   } </script>  <select onmouse = "openwindow()">   <option id = "a" value = "a">a           </option> </select> 

so basiclly im trying nesting select inside select.

obviously cant done this, 1 has idea how can done or if use jquery (i not familliar it) how can done?

thanks.

i couldnt find 1 explains in best way, can see every category has option subcategories.

there no onmouse event only. use onmouseover or in mouse events category on this page.