>>> 1 Undefined behavior:
>>> BEHAVIOR, upon use of a nonportable or erroneous program construct or of
>>> erroneous data, FOR WHICH THIS INTERNATIONAL STANDARD IMPOSES NO
>> (Emphasis added.) This definition only adds to the confusion.
> (To be fair, this means that the definition is grammatically incorrect
> according to the formal rules of academic English. The commas should have
> been omitted, as the appositive phrase "upon use of..." is essential to the
> meaning of "behavior.")
I completely agree with Roberto that the sentence is confusing. And (I
guess) especially for us non-native English speakers (Roberto and I, I
mean), because, as you pointed out, it is grammatically incorrect. At
least the first comma should be omitted.
May be the initial intent was to make the part between commas as an additional "side note" of application of that definition.
But instead of surrounding it with these two commas, they could have used parentheses:
> 1 Undefined behavior:
> Behavior (upon use of a nonportable or erroneous program construct or of
> erroneous data) for which this international standard imposes no
The essential parts of the definition are effectively before the first comma and after the second one, without sacrificing clarity.
Maybe the parentheses were there, but a reviewer thought that replacing everywhere around parenthetical text the parentheses by commas was better style (but it is only true when the parenthetical text occurs within a plain verbal sentence. And this is not the case here with just a nominal phrase part of a definition list
This is a minor issue anyway: there's no other way to interpret this text, given the context: the fragment starting by "upon" can only attach as completing what is before, there's nothing after that fragment that "upon" could complete.
Dropping the two commas would be worse than restoring the intended parentheses. and using emphasis with ALL CAPITALIZED TEXT is bad style, even if the IETF and some other standard bodies uses it for very limited words related to conformance, such as occurences of MUST (NOT), SHOULD (NOT), MAY (NOT), and otherwise some contractual terms or denial of warranties (capitalizing long sentences make them almost unreadable (and inapplicable in most languages, including those written in bicameral scripts):
It's much better to denote emphasized or parenthetical text by other means such as: indentation, decorations (e.g. asterisks, surrounding box) before/after/around the text, or other rendering styles (font size, bold, italic, colors... or "small-caps" preserving all grammatical differences of capitalisation and all diacritics) if the support format permits it.