|Keep It Simple, Stupid|
Well done! This gives a good overview of Perl's quoting constructs. IMHO, it should keep being that -- an overview. The details are documented in perlop and there's no reason to double document it. If perlop isn't clear enough let's make improvements to that document instead. So my real intent of this reply is to request that you start the document by stating what it's for and saying that the details about quoting in Perl in found in perlop.
This below is just details and I'm not sure whether or not this should be included in this document, but perhaps the text should be adjusted to not contradict them.
Here-docs can also have backticks around them, and they will then execute the commands in it. I've never seen this used, and since I'm not a fan of `` nor qx() (but like readpipe()) I really don't like <<`CMDS`. It's just sick.
The second detail is that all chars, except whitespaces, can be delimiters.
prints, as expected (?) "Hello World!". If it's an alphanumeric delimiter a whitespace between it and the q is required.
You call q() a function. I believe it's more correct to call it an operator.
As an editorial change I'd prefer to see all Perl bits wrapped in code tags, even a single q if the Perl operator is referenced, but that's very much a matter of taste.
Again, well done!
See perltoc if you don't know which perldoc to read!