Hi Carsten,
the only way to understand this paragraph is historical.
I guessed it, thanks for making that clear.
In the early days of BEAMER export, Eric Fraga invented a way to make
columns using an additional level of outline structure, just for
making the columns.
http://thread.gmane.org/gmane.emacs.orgmode/19895/focus=19895
Interesting.
This worked, but made it difficult to export this file in any other
way, because of the extra structure. This was overcome with the
BEAMER_col property, and this is what this paragraph and the phrase
"without additional structure" is referring to.
Ah, ok. So now you don't need an extra outline structure for making a
*columns* environment, but you still need it for ending the last
*column* and starting a new one.
I've though I could go without the latter, too. That would be good
for
documents you export as presentation but also as article handout.