Not sure that completelly get the point. You want the user to be able to type only some limited number of chars? And then to choose from list only?
I want the user to be able to type in and select only items that appear in the drop down,
or in other words, for the combobox/suggestionbox to only accept input from the drop down.
if the drop down contains the following values:
The user will not be able to type in "P" or "Ji", only prefixes (and eventually all) of the items that appear in the drop down.
Hope this is clearer.
We eventually ended up using the combobox component and validating the input using a JS "onchange" handler.