I am trying to search for
XYURLGenerator, which exists in the comments here.
Why won't StackOverflow find these questions?
Comments are not indexed in the search. Comments are ephermal, and are prone to deletion at any time -- they only need to be used for suggesting clarifications to the post. No real need to make them searchable.
Generally, you may use Google to find these, though that comment is too new to have been indexed. It probably will be by tomorrow.
According to this question, you can't search comments directly. This still applies today.
Hugo Dozois is correct, comments are not indexed in the search. This is because they are not intended to be permanent, and should only be used for minor clarifications.