I posted it only because I thought it might be helpful to others to note the subtle "gotcha" between defining variables with "my" and with "local" when using a construct such as $$ctm.

right, but my point was that if they don't use that construct, and instead use a safer, more robust, versatile, and maintainable construct, then the "gotcha" doesn't even exist ... IMHO I just saw it as recommending that one wear gloves when punching a wasp nest out of a tree -- the first thing anyone is gonna ask is "why aren't you using a ten-foot pole?".
As quoted from the article (it's a good read if you haven't yet) i mentioned above, (Summary #2) Being careful does not mean trying to understand the possible consequences while behaving dangerously; it means avoiding dangerous behavior in the first place. Don't say ``I know it's dangerous, so I'll be really careful.'' Say ``I know it's dangerous, so I won't do it.''