If you have selected multiple records before opening the Asset Information window, you can change the field values for multiple records at once. But this is only possible, if in your User Settings for the Display of the Asset Information window the option Only One Windowis activated and Display values identical for all selected records is checked.
If the asset information of multiple records is shown in one window, only field contents which have the same values are displayed. So the Asset Reference and Thumbnail fields will always be empty. Check boxes (Boolean fields) with different values appear gray. The field Categories only displays categories that the selected records have in common. All other field types are displayed with no value if there are different values for fields.
Fields with different values do not show a value but can be edited – this also applies to gray (neutral) check boxes. If you add an additional category, this category is added to the set of categories for each record.
If you add any text to a field that already contains values for one of the selected assets, you are asked whether you want the new text to replace the existing value or to be appended to the existing text.