Currently, in our source code, some code that assists controllers can be found
in classes named "Service":
Some of these classes are Transaction classes that need to be renamed, and some
of them are utility classes.
/src/Services/SanitizerService.php is the best
example for that.
Some code in the services should rather go into the modules if they belong to a specific module.
Also see the section Services for a broader use of this term.