The script expects aliases to be defined like this in the RST docs:

    my.alias ``VCL <= 4.1``

        Type: DEPRECATED

	Alias of: something.else

	A little description is still necessary.

There is no DEPRECATED type in addition to the SYM_ALIAS kind, this
is a purely cosmetic suggestion.

Deprecated aliases should probably have a high VCL version limit like
in the example above, generate.py doesn't enforce it so far.