Tag Libraries are a recent addition to JSP and have been quickly adopted by the development community. As with all new technologies, Tag Libraries are rapidly developing and changing.
As you saw in the section on cooperating tags, it is easy to write generic tags that provide useful functionality, such as iteration. Many Tag Libraries provided with JSP-compliant Web servers include their own custom tags, many of which are generic tags.
The proliferation of different Tag Libraries providing similar features has been seen as a problem, and the Java Community Process (JCP) is working on a standard set of tags to be included in the JSP standard.
The JavaServer Pages Standard Tag Library (JSPTL) is Java ...