Multiple header sources for an index.header query prefix?

[Keith Amidon <camalot@picnicpark.org>]

I've been a very happy user of notmuch for a very long time. Thank you 
for such a great tool!

Recently I've been working on implementing a new workflow for handling 
email which uses automated tagging much more heavily. In doing so, I 
want to use some custom header indexes to construct some of the searches 
and it seems like it would be very convenient to be able to index 
multiple custom headers under the same query prefix. For example, I'd 
like to be able to index both X-spam and X-Spam-Result under the query 
prefix "Spam:".

I tried just adding two custom header lines to the config file with the 
same query prefix, like:

[index]
header.Spam=X-Spam
header.Spam=X-Spam-Result

It appeared that after reindexing, notmuch just used the final line with 
the same query prefix. In addition, the python bindings config parser 
fails on such a configuration with an error that the header value is 
already in use. Checking the code, it this behavior seems consistent.

I started thinking about how I would add this feature and was thinking 
it might be better to support in the configuration by using semi-colon 
separated values like some of the other config options. For example:

[index]
header.Spam=X-Spam;X-Spam-Result

Does this seem a reasonable way to go? Is this an extension of the 
custom header indexing behavior that you would be interested in? 
Finally, any suggestions for approaching an implementation? In 
particular, I believe there were some recent changes to also store the 
configuration in the database. Any thoughts on how this suggestion would 
interact with that?

Thanks for your help!

Regards, Keith