Passing Data Between Nested Custom Tags; Variable Scopes And Special Variables - MACROMEDIA COLDFUSION MX 61-DEVELOPING COLDFUSION MX Develop Manual

Nested custom tags operate through three modes of processing, which are exposed to the base tags
through the variable
•
The start mode, in which the base tag is processed for the first time.
•
The inactive mode, in which sub tags and other code contained within the base tag are
processed. No processing occurs in the base tag during this phase.
•
The end mode, in which the base tag is processed a second time. The end mode occurs when
ColdFusion reaches the custom tag's end tag.

Passing data between nested custom tags

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:
•
What data should be accessible?
•
Which tags can communicate to which tags?
•
How are the source and targets of the data exchange identified?
•
What CFML mechanism is used for the data exchange?
What data is accessible?
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.

Variable scopes and special variables

Use the Request scope for variables in nested tags. The Request scope is available to the base page,
all pages it includes, all custom tag pages it calls, and all custom tag pages called by the included
pages and custom tag pages. Collaborating custom tags that are not nested in a single tag can
exchange data using the request structure. The Request scope is represented as a structure named
.
Request
thisTag.ExecutionMode
:
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