Use alt for replace prompt, be more consistent...
light prompt : test read-key-sequence-vector

code a ~nu-check-vector for this.
commit 522a58a30f5864d868c85f2318b72eb166f485ab did
change tab recognition. But actually as a string,
tab has several representation given ... some criteria
I don't know.

Best is to check for 'tab. Thus, we need a vector.