[I am a SSIS newbie.] Can anyone refer me to official Microsoft
documentation on how to dereference SSIS variables, and in what
contexts they may be invoked? For example, the documentation might
state, "if you have defined a variable named 'ExcelFile' then to refer
to it you would enter @[User::ExcelFile] instead of the absolute file
path."

I have seen this syntax only in non-MS sources. As a reference, a text
search for '[' on the MS SSIS page "Integration Services
Variables" (http://msdn2.microsoft.com/en-us/library/ms141085.aspx)
does not find any matches. Neither do searches on any of the linked
pages under "Variables How-to Topics (SSIS)" (http://
msdn2.microsoft.com/en-us/library/ms141105.aspx).

Many thanks for any help.

-- Josh