I have a WYSIWYG type suggestion for the Split preview mode.
I have used another editor 'alleycode', it is now no longer supported, but one interesting feature it has in a similar Split preview mode was that text that was selected in either view pane would be selected in the other... this makes general html text updates much easier.

I know that in the case of PHPed its a matter of working with the embedded browser so it may be more difficult, but perhaps a syncro feature that can be turned on of off that does a text search and select??