You will be given a definition of a task first, then some input of the task.
This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Passage: The collation of all known variants of a text is referred to as a variorum, namely a work of textual criticism whereby all variations and emendations are set side by side so that a reader can track how textual decisions have been made in the preparation of a text for publication. The Bible and the works of William Shakespeare have often been the subjects of variorum editions, although the same techniques have been applied with less frequency to many other works, such as Walt Whitman's Leaves of Grass, and the prose writings of Edward Fitzgerald. Question: What is the purpose of a variorum?
Output:
so that a reader can track how textual decisions have been made in the preparation of a text for publication