checkdoc-verb-check-experimental-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 to attempt to check the voice of the doc string.
This check keys off some words which are commonly misused. See the
variable `checkdoc-common-verbs-wrong-voice' if you wish to add your own.

You can customize this variable.