|Synonyms:||metadata, meta tags|
|See also:||Labels, Warnings|
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A formal set of tags may be a "taxonomy" or "controlled vocabulary". Most fandom tags are informal and uncontrolled, known as a "folksonomy".
Archive Of Our Own combines these in a complex and labor-intensive but effective Tag Wrangling process, which allows creators to tag as they please but then marks many tags as synonyms for a canonical tag. This allows readers to find or filter out fandoms, pairings, and topics without having to indicate each one individually. Other tags are "free form" and not included in the wrangling system. Early versions of this system were inflexible and frustrating, partly for technical reasons but also volunteer and policy issues, leading to extensive AO3 Tagging Policy Debate.
Tumblr Tagging is completely free-form and idiosyncratic. Hashtags are used for finding fandom discussion, identifying fanworks, post blocking, and commentary. Tumblr tags are visible in post notes but no longer automatically retained during reblogging, which makes them ephemeral and personal.