What is the definition of Code Properties?

[SHND]

I understand this is a translation from another repo, but from the text I couldn't fully understand what code properties mean. We have below in the text:

In functional programming, where there's an emphasis on code properties rather than implementation details, the map operation is interesting due to its limitations

I have some guesses but What is the actual definition of term Code Property?

[Enrico Polanski]

I understand this is a translation from another repo, but from the text I couldn't fully understand what code properties mean. We have below in the text:

In functional programming, where there's an emphasis on code properties rather than implementation details, the map operation is interesting due to its limitations

I have some guesses but What is the actual definition of term Code Property?
Code properties are defined generally as function properties with their domain and image.