What I'm trying to say at the title is, I have this Select List field that gets its values from a taxonomy called "Thing".
The taxonomy term are (Thing-1,Thing-2,Other). When "Other" is selected a text field called "Specify" will appear. What I'm trying to do is when the user submits the form. Whatever he placed on the "Specify" field will be added as a "Thing" Taxonomy term.
So the terms will be (Thing-1,Thing-2,New Thing,Other).
I might be over explaining this, but I can't find anything on google.