On Mac OS you might need to scroll the tabs to the right to see the Content Handlers tab.
As shown below, two content handlers have been configured, one for TextViewer and one for ImageViewer. The Windows tab is on the top, and the Mac OS version on the bottom.
To create a new content handler, press Add, or to edit an existing content handler, press Edit. Both actions open the Content Handler Properties window. See Defining Content Handler Properties.
To adjust the order of the content handlers, select one and using the Move Up and Move Down buttons. To remove a content handler from the list, select it and press Remove.