Convert text book to frame?

What I want to do in Pages is to create a text box that is locked in position, but whose content can be changed.

In a word processing document in AppleWorks, one could create a text frame and lock it. One could still type whatever one wanted into the frame, or alter whatever was there already, while the position of the frame remained locked.

In MS Word , one can create a text box and convert it to a frame, which behaves like a locked frame in AppleWorks.

In Pages, I have neither found a way of doing this nor found any reference to such a thing in Pages Help or in the downloadable Pages 09 Manual. My version of Pages is 4.3 and seems to date from March, 2012; the online Help and the Manual are out of date.

Any help would be much appreciated.