I was just looking for a solution to this... how timely! The closest I found to being able to have an "apple-defined placeholder" is by following all your steps (editing master, making new text box), but then doing the following:
1) select the text box
2) go to the "Format">"Advanced" menu and select "Define as Text Placeholder."
This isn't the same, since the text will always show up on the slides (as opposed to only showing up if YOU wrote something in the box... you can delete it if you want, but its not the same as apple's default), but it does have the functionality you want. I hope this helps you!
EDITED TO ADD:
...aaaand the age-old trick of reading the
manual works again. Go to page 188 of the linked document and you'll see that there's a different way to do it. In short:
1) Make a text box in a master slide, keep it selected.
2) In the Inspector, go to "slide inspector" (second from right), and select the "appearance" tab.
3) Check the checkbox next to "Define as Text Placeholder." Assign it a tag.
For me, I found that once I did this, I could delete the text inside the textbox and it wouldn't automatically be deleted. I assume that assigning it a tag has something to do with that. I still don't know how to get text to automatically show up in the textbox... that seems to be a special functionality reserved for the apple-defined boxes. Again, I hope this helps!
Message was edited by: Eliezer Kanal