You might use a line condition to accommodate an unstable data page structure. For example, consider a document that uses ASCII emulation and for which the data selection you want does not always appear in exactly the same place on every data page; the data selection shifts up or down by a few lines. The string “PREF” appears on those data lines, making it possible to uniquely identify them. You create a data selection object that spans the entire area in which the data selection can appear, and set a line condition to test for the presence of the string “PREF.” The data selection applies only to those lines in the data selection region that contain the string “PREF.”