I want to be able to use Autocomplete's for strings separated by commas, semicolons, etc. So if a user has a grocery list string and every item is separated by a comma (Apples, Bananas, Cheese, ...) I want them to be able to use the auto complete to quickly find items quicker (think more along the lines of specific brands, quantities, sizes, for every item) and still build out their list of string. 
So the user would have something like: 'Cupcakes (12 count), Mozzarella Cheese - Kraft, ...'
So the autocomplete would filter the string to find the part after the last comma and use that to search, but when the user finds their item and selects it, it needs to append to the string (and add a comma) and not overwrite it. Then continue the cycle.

Attempting to use OnChange does not allow for this to happen. On selection of a dropdown item, it will overwrite the string entirely.