what is id in ValidationMessage?

[Jeya Balaji]

Hello all,
I am using tomcat 4.1 and jdk 1.3
While validating custom tag lib, the validate method of TagLibraryValidator should return ValidationMessage
The api describe the constructor like this :

public ValidationMessage(java.lang.String�id,
                         java.lang.String�message)
Create a ValidationMessage. The message String should be non-null. The value of id may be null, if the message is not specific to any XML element, or if no jsp:id attributes were passed on. If non-null, the value of id must be the value of a jsp:id attribute for the PageData passed into the validate() method. 
Parameters:
id - Either null, or the value of a jsp:id attribute.
message - A localized validation message.

I am not very clear about the jsp:id. Should I pass a string (like "<mytag:foo>") which will indicate the tag causing the problem?
What is the meaning of "If non-null, the value of id must be the value of a jsp:id attribute for the PageData" ?
Thanks,
Balaji