This Zone type allows you to select a specific area of content and provide it with separate attributes. For example, you can select a List that is arranged in several columns within a normal page of text, and select Div from the Type drop-down box in the Zone Tab. You may edit the div without influencing the remainder of the page - you can re-order the contents of the div (select Re-order this div from the Sub-Reading Order section of the Zone Tab) in a different format than the rest of the current page.
To change the Sensitivity of ONLY the contents of the Div, create your Div, then go to Zone Properties in the Zone Tab and select Sensitivity. This will change to the Sensitivity Slider in the Zone tab and allow you to alter the sensitivity of only the content within the Div.