I currently use the Extra field to enter multiple lines of information on the type of media an item is stored in.For example, I may have a book as both a hard copy and a Kindle edition, so I enter this in the Extra field.This is fit for this specific purpose but is not sortable and becomes clumsy if different and multiple pieces of information are combined in the single Extra field.For example, I have American military attaché reports circa 1939-1940.Some documents are reports from the UK, other reports from France, others may cover multiple countries.With a an open "Extra2" field, I could use it to identify the geographic coverage of the report.An alternative is to create folders, but adding a field is, to my mind, a more efficient way than further expanding and complicating the folder structure.
Upgrade Storage
Does this address your use case?If not, can you describe what you want to achieve?