Personal canon

A personal canon, also known as a headcanon (or a more limited personal continuity), is one fan's interpretation of the Transformers mythos. This can range from picking and choosing stories and characters that they favor and assembling them as they like, to discarding one or two distasteful properties from an otherwise accepted continuity. A personal canon can also be various events from different universes brought together into one single storyline (e.g. G1 and the Unicron Trilogy in the same universe).

This is often used in fan fiction, where an author will use an established continuity up until a certain point, from which they would start telling their own stories. Motivations for these stories can range from a desire to retcon another story that the author dislikes, or to curiously pursue a 'what if' continuity based on a key event happening in some different way. These are typically referred to as "AUs", an acronym for Alternate Universe.

On a more simple level, personal canon can refer to an individual fan's overall preference for certain interpretations of the Transformers mythos over multiple continuities, such as saying "Quintessons are cool, as long as they didn't create the Transformers", or the acceptance/assumption of the popular retcon that Transformers have sparks in all timelines.

When fans make it to the big leagues and become official creators on the franchise, they may end up canonizing their own personal theories.

Common examples of personal canon

• Accepting some seasons of a continuous show or some shows in a sequence of shows, but not others. Examples: only accepting the first two seasons of the Generation 1 animated series, but not the subsequent ones. Or only counting Beast Wars, but not Beast Machines. Or counting Transformers: Prime but disregarding Robots in Disguise. Or Earthspark having a single, one-off season.
• Having one's fan-favorite characters survive their depicted deaths. Examples: saying that Brawn survived The Transformers: The Movie or Nightbeat survived Marvel's Generation 2 comics.
• Renaming unnamed characters after ones who fulfill similar roles in another continuity.
• Disregarding one animated-series origin of the Constructicons for another (or concocting a way for them to work together somehow).
• Merging elements of the comic and cartoon adaptations of a continuity, such as Dreamwave's Armada comic and the Armada anime.
• Regarding Decepticons being descended from the Liege Maximo or Quintesson military hardware (and thus being intrinsically evil) as antithetical to the concept of the Civil War being political and that wartime factions were chosen through the exercise of free will.
• Accepting everything in every known Transformers continuity as having happened as a single jumbled entity, ignoring the inconsistencies as "gray areas" that one mustn't be concerned with.
• Considering one's own (or somebody else's) fan fiction as a part of continuity.
• Incorporating authorial intent and other pseudocanonical sources into one's interpretation of a story.
• Taking one's favored pairing as canon... And waging flame wars on anyone who disagrees.

And so on. There are, of course, infinite possibilities.