Screw thru electric box - against CODE ??????

I just read an article in Popular Mechanix or Family Handyman advertising a plastic electrical box that now allows you to screw it to a stud from INSIDE the box.
The article went on to state that it is against code to put a screw thru ANY PART of the INSIDE of a box to hold it to a stud or whatever.
Since I have done this ( screwed the box from inside to studs/walls ), does anyone have any idea WHY it is against code ?
Is there some fear of the screw contacting electrical wires, etc. ???
I fail to see a problem. Obviously I am not an electrician.
TIA
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I fail to see a problem either!
I've spent some time reading the NEC, certainly wouldn't claim to know it completely, but all I can recall is that boxes have to be "securely fastened". No specifics on how.
It's pretty common to see metal boxes screwed either directly to concrete walls, or on furring strips. Seen quite a few nailed to overhead floor joists in basements, too (height permitting).
And my last argument: if you're not supposed to do this, why do metal boxes have all those holes in them?
Thinking about it a little more, I've always seen this with *metal* boxes. Maybe they don't want you to do it with plastic boxes because if you overtighten the screw the plastic might crack?
Eric Law

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