- The Yahoo! toolkit has it’s own animation library, it’s own drag and drop library and it’s own XmlHttpRequest wrapper, just like other libraries like Dojo and prototype.
- The Yahoo! UI Controls depend on Yahoo’s Core Utilities. The libraries are modular, but not polymorphic with other these libraries.
- The code was released under an open source license (BSD).
All these different implementations of the same core set of capabilities at best means learning lots of ways of doing the same thing and at worst means incompatibility between components from different libraries.