JMdictProject
commented
6 months ago A page is being developed on the project Wiki which covers these tags, The text of this issue has been transferred there. See: https://www.edrdg.org/wiki/index.php/Kanji_and_Reading_Information_Fields
[An "issue" is being opened for each of the kanji/reading tags to provide a forum for discussing the definitions and criteria for applying the tags. It is intended to be used to assist in the preparation of documentation of the tags.]
The [iK] tag is associated with kanji forms and is currently defined as "word containing irregular kanji usage". It is currently used in 652 entries. It probably should be redefined as "form containing irregular kanji".
The purpose of the tag is to inform users that one or more of the kanji in the surface form is not correct. The tag dates from the early days of the project and is typically associated with kanji which appear very similar to the correct one, for example the 旧弊 entry also has the 旧幣 form with an [iK] tag.
Most instances of the [iK] tag can probably replaced with the more recently introduced [sK] tag as there is little reason to keep these erroneous forms visible.
There are cases where the tag will continue to be useful. For example, in the 痤瘡 (acne) entry, the 座瘡 form is also included. This form was commonly used, along with the ざ瘡 form, as the correct "痤" kanji was not initially available in the kanji character codes. As the 座瘡 form is still widely used, it probably should continue to be visible.