Answers to coding questions often use a minor change to the example code. But because it's code, you cant emphasize those differences with markdown syntax.
See example below where I've done some gymnastics to show a diff:
Why isn't his working?
<htwl> <body> document </body> </html>
Ah, just a typo. You meant:
In the above example answer, I used a quote block instead of code block, and
<del> to strikeout the old line, and HTML character entities (including
for indentation) to make sure the HTML didn't render as HTML. Painful.
I don't necessarily need to see a full diff, (as in git) where the old line is red and in ~strikeout~ and the new line is green. But it would be nice to give some sort of indication within a code block to emphasize or hi-light a particular change, to focus attention on that line. But of course, you cant use markdown inside of a code block!
That could really be anything: the ability to make a line bold, or a different color, or put a little arrow outside the left margin of that line. Anything to focus attention to certain lines.