Some Problems in Understanding in Celestia

Hi, Everybody! I am researching Celestia, reading their Blog and there are some misunderstands for me. Hope you guys can explain it:

  1. When I read “Rollups as Sovereign Chains”, they have mentioned about " enshrined settlement layer". What does it mean? I can not get it.

  2. I have a confuse about the difference between Execution-layer (in the Celestia Docs) and Execution chain (Settlement layers in the modular stack - #3 by Kartik). Can somebody explain it more details for me, please?

Thank you in advance!