well... on very first thoughts.. this is what i think -
tei stands for "tag extra information"
so <tei-class> means a class that give some extra information to a tag.
now the question is, which tag ? the pbvious answer is - your tag.
so to sum up -
"when you use the tag "myTag" in your JSP, the tag handler that will be executed is "MyTag.java" and the <tei-class> element is like telling the container - 'when MyTag.java will run, it will need some extra information, that should be picked from MyTagInfo.java". to add to this - from my experience at job - if MyTag.java doesnt find the tei class you are sure to get a
run time error when the page is requested.
this does sound logical for me (i didnt google, nor did i found anything in the servelt/jsp specs)
correct me if i am wrong