i think, there is no such solution for php. Because html generators (like dreamweaver, fontpage etc ...) display the "draged or droped" things on your screen. But how should it be made in php ?!
in html it is possible because html is a language used to display certian things.
But thereis an editor (coded by Zend Tech., which completes certain php tags when you start typing one which is recognised in their database.)
e.g you type :
mysql_nu
and then a popups shows up and gives you (a few) function beginning with these letters. after pressing enter you get mysql_num_rows or whatever you have selected pout of the popup.
(i testet on a downlaodable version of that program, which i got from zend.com)
maybe it is a little help to you
regards and good luck waiting or searching for a editor which you look for
ali