As of June 2008, the footnotes system supports the separation of references into groups. This allows groups for explanatory notes, table references and the like. See WP:REFGROUP.

The general format for the reference tag would be:

And for the reflist:

There are three pre-defined group names that will automatically cause the link labels and this template to display other characters instead of numbers (see List styles above). These are: "lower-alpha" (a, b, c...), "lower-greek" (α, β, γ...) and "lower-roman" (i, ii, iii...).

See also bug combining grouped references and columns