Most of the functionality is provided by the tags themselves - so no, you don't need to know about the implementations. The only exception is LoopTagStatus which provides a way to get extra information about a loop. So I would learn the basic methods on that interface (they're mostly obvious, like getCount(), getIndex(), isFirst(), isLast() etc.) and be prepared to use them in EL. For example, you should be able to predict the output of the following:
Charles Lyons (SCJP 1.4, April 2003; SCJP 5, Dec 2006; SCWCD 1.4b, April 2004)
Author of OCEJWCD Study Companion for Oracle Exam 1Z0-899 (ISBN 0955160340 / AmazonAmazon UK )
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