The varying and meandrous style of the "guslari", whereby the text of a published poem would not match word for word with that sung during a live performance, is due to the nature of epic poetry recitation itself. According to Slavic studies professor David A. Norris, the "guslar" "did not know his songs by heart, but as compositions made up of traditional phrases and formulaic expressions on which he could call each time he sang. His repertoire was based on a type of rapid composition recalling these fragments and lines and guiding them into place for each performance." This gave "gusle" players such as Višnjić the ability to alter the content of their epic poems depending on the audience or occasion. The liberal use of artistic license also permeated the epic tradition.