checkdoc-spellcheck-documentation-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 run Ispell on text based on value.
This is automatically set to nil if Ispell does not exist on your
system. Possible values are:

nil - Don't spell-check during basic style checks.
defun - Spell-check when style checking a single defun
buffer - Spell-check when style checking the whole buffer
interactive - Spell-check during any interactive check.
t - Always spell-check

You can customize this variable.