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Field ID (1) - showing unique Jira ID of particular field. It might be helpful for solving issues, if there is no data visible, but you are sure this is the correct name → maybe it is the field from another project (field scheme) with same name but different ID. Field IDs are also used in: Templating
Prefix (2) - adds the value set in Templating feature to field ID, making it easier to copy and use in template. When you start using templates, being able to copy the exact field ID with prefix will save you a lot of time, learn more about: Templating
Column (3) - this allows you to acquire the location of particular fields in your spreadsheet, given with exact indexes of the columns. Such a piece of data can be found for every field for which Show button was pushed. Hidden fields have no such information (because - in fact - they don’t exist in your spreadsheet, thus it’s obvious they have no column assigned), so in order to make it appear, you need to push Show button for them as well. Furthermore, by clicking aforementioned indexes we are navigated straight to where these columns actually are in your spreadsheet. For example, if we click G within Assignee box, the name first cell of G column will be selected, exposing its exact location.
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