*Modifiers* refer to any prefixes (first elements of compound queries)
that are neither operators nor fields.
+``(regex`` *atom* ``)`` ``(rx`` *atom* ``)``
+ Interpret *atom* as a POSIX.2 regular expression (see
+ :manpage:`regex(7)`). This applies in term fields and a subset [#not-phrase]_ of
+ phrase fields (see :any:`field-table`).
+
``(starts-with`` *subword* ``)``
Matches any term starting with *subword*. This applies in either
phrase or term :any:`fields <fields>`, or outside of fields [#not-body]_. Note that
.. [#aka-bool] a.k.a. boolean prefixes
+.. [#not-phrase] Due to the implemention of phrase fields in Xapian,
+ regex queries could only match individual words.
+
.. [#not-body] Due the the way ``body`` is implemented in notmuch,
this modifier is not supported in the ``body`` field.