See help for `message-citation-line-format` for details.
-## What are sexp queries
+## What are sexp queries?
For the syntax of sexp queries, see [the manual
page](https://notmuchmail.org/doc/latest/man7/notmuch-sexp-queries.html).
The boolean prefix searches (see Boolean and Probabilistic Prefixes in the man
page), such as tag: or path: searches, need an exact match.
+For [specific
+fields](https://notmuchmail.org/doc/latest/man7/notmuch-search-terms.html#search-prefixes)
+it is possible to use regex searches (although these are often
+noticeably slower than native Xapian queries). The limited set of
+fields is a quirk of implementation which requires a Xapian "value
+slot" in the database schema. Adding regex support for more fields to
+would require of adding more value slots to the schema. The
+performance impact of that needs to be experimentally evaluated, and
+assuming it is not too bad, some database upgrade code would need to
+be written.
+
## How do I search for folders or paths with spaces?
The spaces in the names must be escaped. For example if you use bash or zsh,