Shibboleth.SSO vs SAML2.SSO in Relying-Party.xml

[Y Levine]

I have had a mental meltdown trying to maintain my understanding on SAML
while our main people are away.

Can anyone explain in layperson words what are the difference between the
following 2 beans in Relying-Party.xml (Shibboleth v3)?

<bean parent="Shibboleth.SSO"
 <bean   parent="SAML2.SSO
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