In addition to expansion at first use, some publications also have a key listing all the acronyms used and what their expansions are. This is a convenience for readers for two reasons. The first is that if they are not reading the entire publication sequentially (which is a common mode of reading), then they may encounter an acronym without having seen its expansion. Having a key at the start or end of the publication obviates skimming over the text searching for an earlier use to find the expansion. (This is especially important in the print medium, where no search utility is available.) The second reason for the key feature is its pedagogical value in educational works such as textbooks. It gives students a way to review the meanings of the acronyms introduced in a chapter after they have done the line-by-line reading, and also a way to quiz themselves on the meanings (by covering up the expansion column and recalling the expansions from memory, then checking their answers by uncovering). In addition, this feature enables readers possessing knowledge of the abbreviations not to have to encounter expansions (redundant for such readers).