Quoth Andrei Popescu on Jan 16 at 10:21 pm:
> This is also interesting:
> $ notmuch count 'debian'
> 65888
> $ notmuch count 'dEbian'
> 65888
> $ notmuch count 'Debian'
> 65887

The first two will match stemmed versions of "debian" such as
"debian's" and "debianed".  However, starting a term with a capital
letter suppresses stemming (because it suggests that it's a name,
which you wouldn't want to modify), so your last query matches only
the term "debian".  This is probably documented somewhere, though I
don't know where.

> Where can I read more about this? (except the source :)

Most of this is in the Xapian query syntax document you found.  Really
we ought to beef-up Notmuch's query syntax documentation.