Certain fields within Anki cards can be designated as immutable. This feature prevents accidental or unintentional modification of their contents during the review process. For example, a field containing core vocabulary in a language learning deck might be protected to ensure it remains consistent across all reviews.
Protecting these fields provides several advantages. It helps maintain data integrity by preventing accidental edits. It also allows users to focus on specific parts of the card without the distraction of being able to change fundamental information. Historically, this functionality arose from user demand for a way to safeguard crucial data within their Anki decks.