Some misconceptions about PHP functions isset and empty

Question 1: Does the following empty array use Isset ($arr [0][' id ']) to determine whether there are notice errors?

Question 2: Does the following empty array use empty ($arr [0][' id ']) to determine whether there are notice errors?

$arr = Array ();//define an empty array

Always thought Isset ($arr [0]) No problem, isset ($arr [0][' id]) there will be notice error, empty judge must have isset before the decision to have notice error!

The fact is that 1, 2 of the judgment is no problem, there will be no notice error, the specific oneself can test, not much to repeat.