When searching, in addition to filtering locked and scheduled messages, add the following filters:

Unread

Undelivered*

Failed*
(display only failed messages)

Contacts
(search only contact names not content)

Content

(search only content not names)

Unknown*
(received from numbers not in contracts list)

MMS*
(display only MMS)

Group*
(display only group conversations)

For dual-SIM devices:

SIM1*

SIM2*

Scopes marked with an asterisk should display results with or without a search term entered.