The unique ID of the item. The ID should not change with time, so two
CKEDITOR.plugins.autocomplete.model.dataCallback
calls should always result in the same ID for the same logical item.
This can, for example, allow to keep the same item selected when
the data changes.
Note: When using a string as an item, make sure that the string does not
contain any special characters (above all "[]
characters). This limitation is
due to the simplified way the CKEDITOR.plugins.autocomplete.view
stores IDs in the DOM.