I realized this ticket is for PuppetDB and not docs.
This came from a bug fix for PE-26106 where there were some interesting PuppetDB behaviors related to regex matching for structured facts. The bug note includes the following language:
"PuppetDB's regular expression matching behaves in surprising ways for structured fact value comparison. For example for the structured fact `os`, a rule that matches `["~", "os", ":"]` will match every node that has the "os" structured fact because the regular expression is applied to the JSON encoded version of the fact value. The classifier's classification doesn't use puppetdb for determining classification, and regular expressions in the classifier rules syntax only support direct value comparisons of string types."