Search notes:

DASL

DASL consists of

the SEARCH method and the request/response formats defined for it
feature discovery through the "DASL" response header and the optional DAV:supported-grammar-set property
optional grammar schema discovery, and
one mandatory grammar (DAV:basicsearch)

Basic steps when using DASL

The basic usage of DASL is

The client formulates a query using the DAV:basicsearch grammar
The client passes the query (text/xml or application/xml) to the server («search arbiter») using the SEARCH method.
The search arbiter executes the query
The search arbiter sends the response back using an entity that matches the WebDAV multistatus format (Status code 207, RFC-4918, Section 13)

See also

DASL relies on the resource and property model which is defined in RFC-4918.

RFC 5323: Web Distributed Authoring and Versioning (WebDAV) SEARCH

Apparently, DASL is used in Outlook's object model method application.advancedSearch.

Outlook Object Model: applying filters