I don't know of any way to turn those messages off.
Aside from staying in Live View, Code View or Split Code/Live, I think you're stuck with them.
Jon and Nancy:
That's disappointing to hear, Jon, that we Adobe subscribers have to be told the same thing, every time we open a .php file in Split View or every time we change from Code View to Split View. Do developers see a purpose in repetitively reminding us of the same thing, hundreds of time throughout a day's work? Can one of you pass along this predicament to the appropriate department?
Nancy: Ignoring a problem is sophomoric, especially when it can easily be corrected by revised programming. That doesn't work at all for me.
In my last 15 minutes of fooling with a variety of views, I believe that I've found a way to prevent those pestering messages from reoccurring repetitively. Try this.
• Click the drop-down arrow to the right of Design View.
• Change "Design" to "Live."
• Switch from "Code" to "Split" view as often as you like; the message will not appear.
Apparently, we must work in "Live" view so we can be spared seeing those messages. Alas, when using "Split" view while the "Live" option is selected, a lot of real estate is put into the "Live" portion of "Split" view, requiring additional scrolling. Nevertheless, I'll take that approach rather than ignore the pestering, reoccurring messages that don't come with an option to "No longer show these messages."
Warren