Where does the function 'getSalesEntityType' come from?

[Guido1982]

I was studying this example from the documentation, and noticed this function called 'getSalesEntityType' that checks the entitytype on the id pulled in from the 'data' object. Since no files were included in this function file, I can't see how where this function comes from, although I can understand what it does from the name, I'd rather have a better understanding so I know what I'm doing when writing my own workflow methods. Can anyone explain?