[Exim] Non-numeric variables in filters

I was looking at the spam-filter when I set it up yesterday, and spent a
lot of time trying to find ways to extract the duplicated information
out into variables. I failed, and truly comprehended the difference
between exim config and exim filter.

In the spam filter, the list of extensions occurs four times, and the
fail-text twice. Adding filtering of .chm in made me want to extract
the pattern out and then just use it with something similar to
${expand:FILTERPATTERN}. Is there no way of doing this? If not, should
it be a feature request or are there compelling reasons to not do so?
Performance?

I'm prepared to accept that I spent an hour or so missing the obvious
solution, in which case I'd appreciate pointers to the relevant bit of
the documentation.

Thanks,
--
HTML email - just say no --> Phil Pennock
"We've got a patent on the conquering of a country through the use of force.
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