Folding: I didn't know that is is possible with emacs
Yes, it is. Splitting the window is more useful, especially when combined with markers (and functions that automatically rotate point between several markers), but folding is also available. There's a minor mode for it, for instance (see, IIRC, folding.el). You can also see a great example of folding in action in Gnus: if you're reading an email message with nested quoting, and you middle click the highlighted portion of an attribution line (or position your cursor there and hit RET, I think), that user's comments are folded or unfolded.
I don't think cperl-mode does anything Perl-specific with folding, though.
Multidocument: yes (not the classic MDI, but recursively split screen horizontally and vertically and change sizes of windows)
That description almost makes it sound as if you can only have as many documents open as you can find space on the screen for at once.
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