TextFieldRenderer

TextField -- two-way binding's write half.

The value shown is read from the data model and the value typed is written straight back to it, so the field holds no text of its own. That is the "immediately write the new string back to the local data model path" the implementation guide asks for, and it is also what makes a field agree with everything else bound to the same path: the formatString in the specification's own 00_formatted-text example updates as the field is typed into because both read the one model.

A field whose value is not a data binding is read-only. A literal, a function result, or an absent value gives the field nowhere to write, and a writable-looking field that discards every keystroke reads as a broken renderer rather than as a payload that asked for one.