Unmentioned are:

• Special sequences such as \n.
• Which characters need to be escaped in which kind of quotes.
• What happens if you escape a character that doesn't need escaping.
• Interpolation of arrays.
• Non-interpolation of hashes, globs and code.
• Special variables affecting interpolation, such as $, (and maybe only $,).
• How to interpolate expressions using "@{[ expr ]}"
• <<marker vs <<"marker" vs <<'marker'.

I'm not saying that any of these things should be mentioned, just that you should consider whether they should be mentioned or not.