Hi Satou
Below are the complete texts
Page 445 says
If the value evaluates to null, the variable will be removed!
Imagine that for the value(either in the body of the tag or using the value attribute), you use ${person.dog} evaluates to null(meaning there is no person or person's dog perperty is null), then if there is a variable attribute with a name Fido, that will be removed! (if you donot specify a scope, it will start looking at page, then request etc)
This one seems working like <c:removeAttribute>.
Here comes the confusion one, the text from page 447
If you donot use optional scope attribute in the tag and you are using var of target, the container will search scopes in the order in which you have come to expect-page, then request etc
Please comment
Thanks