ruby-psych 3.1.0+really3.1.0-1build6 (amd64 binary) in ubuntu impish

 ruby-psych is a YAML parser and emitter. Psych leverages libyaml for its
 YAML parsing and emitting capabilities. In addition to wrapping
 libyaml, Psych also knows how to serialize and de-serialize most Ruby
 objects to and from the YAML format.
 .
 Psych has been included with the main Ruby implementation since 1.9.2,
 and is the default YAML parser from 1.9.3 and beyond.