The names of Haman’s ten sons are written on a single page in the Megila, and therefore, in most Megilot, they are written in large print. If they are written in normal size, there would be blank space on the page, which could disqualify the Megila according to some opinions.
However, the Vilna Gaon (Rabbenu Eliyahu of Vilna, 1720-1797) maintained that since there is no tradition requiring writing the names of Haman’s sons in larger print, it is preferable to write them in the ordinary size. There are some letters in the Megila which tradition requires writing bigger or smaller than the rest of the Megila, but no such tradition exists with regard to the names of Haman’s sons. Therefore, the Vilna Gaon argued, it is preferable to write them the same size as the rest of the Megila. In order to avoid the problem of empty space, the Gaon recommended writing the entire Megila with only eleven lines on a page, so that the names of Haman’s sons take up an entire page. Most Megilot are not written this way, and it is certainly acceptable to use a Megila that is not written in this fashion, but one who is looking to purchase a Megila should bear in mind that there is a Halachic preference for an eleven-line Megila.