From
JSP 2.0 spec, JSP.8.5.1, about dynamic-attributes attribute:
The value identifies a page scoped attribute in which to place a
Map containing the names and values of the dynamic attributes passed during this invocation. The Map must contain each dynamic attribute name as the key and the dynamic attribute value as the corresponding value.
In tag file you access to these implicit scripting variables:
request
response
jspContext
session
application
out
config