Part $1$: What would be a good reason to NOT validate a form element on$-$the$-$fly?

In some cases, it will annoy or confuse the user if you are validating and possibly changing values in that element as they are still editing it$.$

The form element is an obscured field like a password.

The form element is required and$/$or "important" for the rest of the input to make sense.

On a form with a lot of fields, it is bettet to do the validation on the server side.

The form element has one or more dependent elements which may or may not need to be presented to the user depending on what value they are entering.

Part $2$: if c$=$"the quick brown hound" what is c$.$substr$(6,3)?$

$"$ck $"$

"ick"

"qui"

"uic"

Invalid syntax.