When you apply any of our modules to a page it can cause an overflow if there is a lot of content in the module displayed.
A good example is the TOC, Table of Contents module. This module, depending on how many pages and headings you have in the manual, will populate a lot of data, causing a red line to appear on the page indicating overflow. Adjusting the number of lines to show allows you to control the overflow and cut it off to continue on to the next page.
Number of lines to show
Adjust the number of lines that you would like to be displayed in the ToC.
The setting "Number of lines to show" in the module appears in many of the other modules as well and is to be used the same as the example above to control overflow.