The _ref suffix looks like a Damianised version of Hungarian Notation. Not the popular version, but the original. The purpose seems to be to help ensure that just by looking at the code, you can tell if it's correct or not. For example, if you have adhered to this naming convention, you could tell at a glance which of the following are correct, and which would result in a runtime error, should that codepath be excersised:
$comments = 'foo'; # 1
$comments_ref = 'foo'; # 2
$comments-> = 'foo'; # 3
$comments_ref-> = 'foo'; # 4
Obviously, then, 1 and 4 are good, while 2 and 3 will result in runtime errors. And that's without seeing any other code. This means you can look at each line in isolation
and be able to intuitively understand its correctness, or lack thereof. That's goodness.
Now, in the original Hungarian notation, these are to be prefixes. But where you put the notation is less relevant than having a consistant, well-defined notation that translates runtime errors into things that are obvious from a simple code-review.