Can autocomplete allow text input outside of the choice list?

[JackTsai]

I have a survey for freshwater fish species records separated by different stations located across Taiwan. Each station has its usual species, but occasionally other species may appear.

We have a full list of all freshwater fish in Taiwan, along with the usual species for each station, selected by fish experts.

I've already set up an autocomplete type with options for usual fish species and now need to provide options from the full list of species. Additionally, I want to allow users to type the name of a fish if it's not on the list, in case a new species is found.

If I don't want the form structure to be too complicated, it could look like this:

1. Usual species list > Other
2. Full species list > Other
3. Other > New species name

Alternatively, could an autocomplete type allow free text input outside of the choice list, like this:

1. Usual species list > Other
2. Autocomplete full species list that can also input free text

[DougBrowning]

We did this with unknown codes in like ASXXXX that we can then fix later.  If you want the list and other in the same field the 3 field trick is a common method.  You basically add a 3rd field hidden in the background and have a if statement to pick the list or the other value.  On mobile but there are a few posts on this on here.