flush-lines has "optional" arguments that aren't necessarily optional

[Joe Corneli]

This is a minor issue, but...

`flush-lines' claims that its second and third arguments
are optional.  However, if the first argument is
present and the third is not, it does a test that doesn't
make sense.  Thus, if the second argument is supplied,
the third is no longer optional.

(defun flush-lines (regexp &optional rstart rend)
 [...]
  (if rstart
      (progn
      (goto-char (min rstart rend))
 [...]

IMO, the function should be rewritten so that both
arguments are truly optional, and both independently
take their default values if the other is not specified.

(flush-lines "foo" (point-min))



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