In principle the right way is to allow any dictionary have option like 'PassThrough' and internal function get_dict_options(dict, option) to check if PassThrough option is true.
Let's consider one example - removing accents.
In the past I always recommend people to use regex functions before
to_tsvector conversion to remove accents, but recently I was noticed that
such trick doesn't work with headline(). So, the only way is to have
special dictionary dict_remove_accent before, which  works as a filter.

I don't remember why do we left this for future releases, though.

On Wed, 14 Nov 2007, Tom Lane wrote:

This patch:
seems simple and useful enough that I think we ought to slip it into
8.3, even though we are far past feature freeze.

As the "simple" dictionary type stands in CVS HEAD, it is only useful as
the last dictionary in a stack, since it never passes anything on as
unrecognized.  With the proposed AcceptAll = false option, it could be
used to filter out some stopwords before feeding tokens to another
dictionary.  While most dictionary types have their own stopword support,
some of them match stopwords after their own normalization processing,
and so there's no way to filter on pre-normalized words.  That seems
like a good improvement, even without the specific need-example that
Jan provided at the start of the thread.

Normally we'd never consider adding a new feature so late in the
development cycle, but this seems small enough and useful enough
to make an exception.  Comments?

                        regards, tom lane

Oleg Bartunov, Research Scientist, Head of AstroNet (,
Sternberg Astronomical Institute, Moscow University, Russia
phone: +007(495)939-16-83, +007(495)939-23-83

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