Definition of the NHibernate Mapping by Code / EF Code First pattern?

Sub-questions:

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  Does this pattern have a formal definition?

  
  


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  Who invented it?

  
  


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  Is it considered a DSL?

  
  

The reason why I am asking is because I would like to better assess its applicability to non-classic-DB scenarios, for example as an alternative to configuration files with a custom format, that don't need to be changeable after compilation.