Intertextual Varieties Intertextuality is classified into three types: mandatory, optional, and accidental. These variances are determined by two important factors: the writer's aim and the relevance of the reference (Fitzsimmons, 2013). If the writer is trying to make a specific point about history, then it is mandatory for that point to be made through using or referencing some form of evidence. If the writer is not aiming to make a specific point but instead wants to include some interesting facts about history, then it is optional for those facts to be connected to each other or not. If a fact does not help to prove or explain something else within the text, then it will usually be considered an accident. Writers can also vary intertextuality unintentionally due to the nature of historical evidence. For example, if a writer is trying to create a sense of mystery around some event in history, then information found in primary sources may often be limited to only what was actually seen or heard about. As such, secondary sources such as books or websites are needed to provide more details about the incident. Finally, writers can vary intertextuality intentionally in order to increase the drama surrounding historical events. If, for example, a writer wanted to show how much history has changed since a certain time period, then he or she would likely use different forms of evidence to do so.