A key custom tag feature is for collaborating custom tags to exchange complex data without user intervention, while encapsulating each tag's implementation so that others cannot see it.
When you decide to you use nested tags, you must address the following issues:
To enable developers to obtain maximum productivity in an environment with few restrictions, CFML custom tags can expose all their data to collaborating tags.
When you develop custom tags, you should document all variables that collaborating tags can access and/or modify. When your custom tags collaborate with other custom tags, you should make sure that they do not modify any undocumented data.
To preserve encapsulation, put all tag data access and modification operations into custom tags. For example, rather than documenting that the variable MyQueryResults in a tag's implementation holds a query result and expecting users to manipulate MyQueryResults directly, create a nested custom tag that manipulates MyQueryResult. This protects the users of the custom tag from changes in the tag's implementation.