Rather, "split" is the same as "split /\s+/"

Actually, it's not. The only way to avail yourself of the magical default split whilst processing other than $_, is to use ' ' or " " in place of the regex. See the first and last examples below:

C:\test>p1
$_ = '   the quick    brown fox   ';;

print join'|', split;;   ## default split no args (leading null field 
+omitted)
the|quick|brown|fox

print join'|', split /\s+/;; ## \s+ includes leading null field
|the|quick|brown|fox

print join'|', split / /;; ## same as split /\s/
|||the|quick||||brown|fox

print join'|', split ' ';; ## Same as no arg split
the|quick|brown|fox
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