Canonicity, which refers to whether or not something is considered to be part of a given universe, is typically a straightforward concept, but the bigger a franchise gets, the more attention to potential contradictions is required. This wiki uses standard inclusive canon rules. In short, all information that comes from the media or creators of the media is canon unless there's some reason it can't be.
Canon priority
When two pieces of information contradict, priority must be used to determine what is canon and what is not. This can be considered in two layers. The media of the source, and the accuracy of the source. More important media will take precedence over side media; for example, a detail noted by a film will be canon over a detail that contradicts the film in a promotional short. Onscreen information will always take precedence over offscreen information, such as producer comments. However, onscreen character comments are not necessarily reliable, as characters can be mistaken. If there's good reason to believe a character is accurate, it can be assumed they are, but if what is seen onscreen contradicts their statements, what we see for ourselves can confirm a character's mistake. When it's unclear which source is more accurate, such as two movies depicting an event in two different ways, the most recent media can be considered canon over the more dated media. This scenario is a retcon. Media that is not intended to be canon will not be considered canon. This can be determined by fundamental canonical errors that preclude the entire piece of media from taking place alongside the other media in the franchise, or meta commentary, such as a character mentioning the existence of a film in the franchise in which they supposedly exist.
- Direct information: Information directly witnessed onscreen is the core method of determining canon details. Direct information is always canon unless it is later retconned.
- Reliable narrator: Information given by an onscreen character who is both familiar with the information they're providing and has no reason to lie about it can be considered canon until and unless the character is shown to be mistaken.
- Producer comments: Comments provided by producers/directors that provide extra context to onscreen details can be considered canon. These may come from social media, documentaries, or other published work from the franchise, such as art books.
- Deleted scenes: Deleted scenes can be considered canon as long as they do not contradict the films/series, and as long as producer comments do not preclude their canonicity. Scenes can be deleted for any number of reasons, one of which is the impact they might have on the canon. This possibility must be considered before determining that a deleted scene is canon.
- Unreliable narrator: Information that comes from a character who is not reliable, such as liars and fools, cannot be considered canon unless reaffirmed by other means.
- Non-canon media: Information that comes from media that is clearly not intended to be canon cannot be considered canon.