This functionality came through a recent addition to the library.
terms/phrases in the body, the subject, or any of the sender or
recipient headers.
+As a special case, a search string consisting of exactly a single
+asterisk ("*") will match all messages.
+
In addition to free text, the following prefixes can be used to force
terms to match against specific portions of an email, (where
<brackets> indicate user-supplied values):
"\tthe given terms/phrases in the body, the subject, or any of\n"
"\tthe sender or recipient headers.\n"
"\n"
+ "\tAs a special case, a search string consisting of exactly a\n"
+ "\tsingle asterisk (\"*\") will match all messages.\n"
+ "\n"
"\tIn addition to free text, the following prefixes can be used\n"
"\tto force terms to match against specific portions of an email,\n"
"\t(where <brackets> indicate user-supplied values):\n"