It is easy to create the select-char markup with [1668, the corresponding PHP function].
There is no need to implement %select-char% a change handler in JavaScript, when you use the %nodes% attribute. This holds a selector of the nodes to be filtered. Each node must have an attribute %data-search% holding the corresponding value.
To combine a %select-char% with an [1495, %input-search%] (like in the Topincs Index), just make sure they are siblings.