checkdoc-force-docstrings-flag is a variable defined in `checkdoc.el'.
Its value is

  • This variable is safe as a file local variable if its value
    satisfies the predicate `booleanp'.

Non-nil means that all checkable definitions should have documentation.
Style guide dictates that interactive functions MUST have documentation,
and that it's good but not required practice to make non user visible items
have doc strings.

You can customize this variable.