Currently, all metadata fields are basically strings, but we are planning to support more specific types (most notably dates and names) with special features and input widgets. For dates, we will be using the upcoming extensions to ISO 8601 (previously EDTF) to support a wide range of date features such as uncertain/approximate dates, date ranges, intervals etc. (if you are interested about the specifics, take a look at edtf.js which was written specifically for use in Tropy). All date values will go into a special index which will allow us to support efficient time range searches in Tropy (probably using an interactive timeline, but we have not finalized a UI yet) and we want to provide a dedicated widget to make input easier. We hope that we’ll be able to support sorting using date columns, but that will be very tricky (because of custom templates, it is not guaranteed that fields like dc:date are indeed date values); this does not apply to special fields such as the creation and modification dates, which will definitely be sortable as dates.
While date fields are not fully implemented yet, you can already benefit from using valid EDTF values in date fields (e.g., ‘2017’ or ‘2017-12~’), because they will be formatted based on the current locale. For example, ‘2017-12’ would be formatted as ‘déc. 2017’ in the upcoming French version. This feature is still experimental and not fully accessible, but a preview of the things to come.