PHP Shell could provide a simple text editor which
allows you to load a file, edit it and save it again.
Editing new files should be possible.
Saving under a different name than the one loaded is
probably not necessary since this is just another way
of doing a copy.
Support for saving the file with UNIX, Windows, or Mac
line-endings could be provided --- loading will work by
itself because \n and \r are treated the same by browsers.