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1) This statement:
If you leave off the pattern, split assumes you want to split on /\s+/.
needs considerable qualification. You can't just 'leave off the pattern' except in one particular circumstance. Try this:
It just doesn't work (at least in 5.6.1). You can only leave off the 'pattern' if you also leave off the 'target', ie if you are splitting on an implicit $_, eg:
2) This is plain wrong:
One special case is when you specify the string literal, " " (a quoted space), which does the same thing as specifying no delimiter at all (no argument).
There is nothing special about " " (see gmax's example above). You are confusing it with ' '.
3) One other minor point, I would suggest bringing the paragraph Preserving delimiters up to just below Where do delimiters go?, which IMHO would be a more logical ordering.
Update: See Abigail-II's post below