a clarification regarding occurrence of assigner and assignee in Policy vs Rule

Respected Madam/Sir,

i am a newbie to ODRL and hence this question.

context
=======

    We see the definition of assigner and assignee as follows:

    assignee
    ========

    :assignee
        a rdf:Property , owl:ObjectProperty, skos:Concept ;
        rdfs:isDefinedBy odrl: ;
        rdfs:subPropertyOf :function ;
        rdfs:label "Assignee"@en ;
        skos:definition "The Party is the recipient of the Rule."@en ;
        rdfs:domain [
            a owl:Class ;
            owl:unionOf ( :Rule :Policy ) ;
        ] ;
        rdfs:range :Party .

    assigner
    ========

    :assigner
        a rdf:Property , owl:ObjectProperty, skos:Concept ;
        rdfs:isDefinedBy odrl: ;
        rdfs:subPropertyOf :function ;
        rdfs:label "Assigner"@en ;
        skos:definition "The Party is the issuer of the Rule."@en ;
        rdfs:domain [
            a owl:Class ;
            owl:unionOf ( :Rule :Policy ) ;
        ] ;
        rdfs:range :Party .

    i.e. the assigner and assignee property can occur for a Rule
    or Policy instance


question(s)
===========

(1) What is the semantic difference between

    (a) when they occur as properties of a Duty (Rule) instance
        as in EXAMPLE 20 of section https://www.w3.org/TR/odrl-model/#duty

    #....
    "obligation": [{
          "assigner": "http://example.com/org:43",
          "assignee": "http://example.com/person:44",
    #....

                    AND

    (b) when they are occur as properties of a Agreement (Policy) instance
        as in EXAMPLE 21 of section https://www.w3.org/TR/odrl-model/#duty

    #...
    "@type": "Agreement",
    "uid": "http://example.com/policy:42B",
    "profile": "http://example.com/odrl:profile:09",
    "assigner": "http://example.com/org:43",
    "assignee": "http://example.com/person:44",
    #...

(2) Can some use-case(s)/example(s) be stated to highlight the difference
    if any ?

(3) please do point me to a message in public-odrl-contrib or
    public-odrl-contrib in case this has already been answered as my
    searches in these groups did not yield the required answer.


thank you

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