Linking and Unlinking Tools  
    The Linking tool forms a connection between text boxes. Text 
 “flows” between linked boxes as if they were one continuous region. 
 This flow of text between linked text boxes is referred to as a “text chain”.
 The Unlinking tool is used to break the links between text boxes. 
    When the Linking or Unlinking tool is selected, the links for the
 active text chain become displayed as soon as you click on a text box. 
    To link one text box to another: Select the Linking tool. Click on the
 box from which you want text to flow.

  Press the Shift key and click on the box to which you want text to flow.
 An arrow is drawn between the “from” and “to” boxes indicating the 
 newly established link.  You can continue clicking on new “to” boxes 
 in this manner,  creating an entire text chain. 
 Note: If you link to a text box that is part of a chain, the box is
 “extracted” from its chain before the new link is made. If your
 “from” box is in the middle of a chain, the “to” box is inserted after it.
You can’t link two boxes that both contain text. 
    To “extract” a text box from a chain: Select the Unlinking tool.
 Click on the text box you want to extract. The links  are shown as arrows.
 Press the Shift key, and click on the same box . This reroutes links 
around the extracted box. Any text that was in the chain remains with the chain. 
    Linking and unlinking on master pages: Text box links can be made
 on master pages as well as on other pages in a document.