What are the IK algorithms that UE is using? (in ABPs, Control Rig)

Hi everyone,
For a while I was wondering how to make a conscious decision regarding what kind of IK algorithms should I use when creating IKs in Control Rig in UE5. There is a lot of algorithms but I’m having a hard time “mapping” the ones in unreal to these available in literature.

Pretty much the only 2 ones that are easily findable are FABRIK and CCDIK, but what about all the Basic IK, 2-3 bones ik, and especially fullbody ik?

Are there any science papers or any other easier to digest papers that explain how these algorithms work underneath? I would like to understand the costs associated with using different methods.