Yes that works – I knew it does – but I was wondering why doing it this way caused such strange output...

I've given thought to operator precedence, but I figured things wouldn't align up and I'd get a warning or error.

So how would this get parsed? Something like the following I presume:

Thanks for the explanation, operator precedence makes a lot more sense now. I'm just surprised things lined up well enough not to cause any warnings or syntax errors.

The thread I've linked to above has an example both for how something very similar gets parsed, and how to find out how it's parsed. Did you not read it?

(defined($var) ? $var) .= ('y' : $var .= 'n') if $el eq 'apple';

No, because there can be no ? without an accompanying :. Thus, the ‘middle’ assignment is parsed as you like (since the tokeniser hasn't seen a : yet, hence knows that it's still inside the conditional), but the ‘last’ one isn't (since the tokeniser believes it's done with the conditional after finding the second occurrence of $var):

(defined($var) ? $var .= 'y' : $var) .= 'n'

(Of course, the statement about every ? requiring an accompanying : is a lie, as regular expressions show; but you know what I mean. :-) )