The component equality matching rules have a variable assertion syntax. In X.500 this is indicated by omitting the optional SYNTAX field in the MATCHING-RULE information object. The assertion syntax then defaults to the target attribute's syntax in actual usage, unless the description of the matching rule says otherwise.
The SYNTAX field in the LDAP-specific encoding of a MatchingRuleDescription is mandatory, so the OpenAssertionType syntax is defined to fill the same role. That is, the OpenAssertionType syntax is semantically equivalent to an omitted SYNTAX field in an X.500 MATCHING-RULE information object.
Unless explicitly varied by the description of a particular matching rule, if an OpenAssertionType Assertion Value appears in a ComponentAssertion its LDAP-specific encoding is described by the <Value> rule in GSER, otherwise its LDAP-specific encoding is the encoding defined for the syntax of the attribute type to which the matching rule with the OpenAssertionType assertion syntax is applied.
The LDAP definition for the OpenAssertionType syntax is: