HI
The text in the Details panel is divided into different text fields, i.e. Desc1, Desc2, Desc3 and we display the text in each of those as though it is one paragraph. These fields don't have a limit in their length.
There are two limits you might face though.
- If create your layer as a shapefile created in, say, ArcMap there is a 256 character limit to text fields, when you edit text fields. That's the reason we provide those multiple text fields in the Shortlist popup (so you can spread your long descriptions over multiple fields to avoid hitting the 256 character limit for any one field) and it is also the reason we don't recommend using shapefiles for Shortlist content if you want to be really wordy like I am in my descriptions (and forum posts!!).
- If you edit your long text fields via the ArcGIS Online web map viewer to add additional text to a field that is already long, there is a limit to how much longer it will let you make that text. So there is no limit (I know of) to how long the descriptive text in a feature service or CSV-based text field can be, but I have noticed that the ArcGIS Online web map viewer does not let me make my really long text fields any longer via editing the field. I'm not sure what the limit is. It lets me make edits to long text fields but doesn't like it if I try and add additional text into them. For this reason for maps with long descriptions I make my edits in the source file (e.g., Excel) that I use to create my CSVs instead of making the edits in the web map viewer, and then upload the CSV into my web map again. (It is also easier to edit text in Excel because you can wrap the text around in the spreadsheet cells using the word wrap format and you can spell check it).
If the above info doesn''t help and your map is publicly accessible, could you share the URL of your Shortlist, or just the URL of the web map, so we can have a look. Or can you provide a screenshot to show what the exact issue you are facing is?
Thanks for your help anyway!