"Pick" documentation?

[dlm <jamshark70@gmail.com>]

Another question -- where do I find documentation on wl-summary-pick?

The manual/info page says only that it applies * to messages meeting the condition -- but, how do you write the condition?

The immediate use case was to select messages in a date range -- I suppose I can use region operations for that, but it raised the question of what you can actually do with "pick." The default field is Body and I found by a lucky guess that From also works. Other fields must be available but I don't see it written up anywhere.

Thanks,
James