One month back I have added a "set" style for maps to libyaml. This is in accordance with the Yaml standard which states that a set notation may be used when all the values of a map are nonexistent.

Who needs to review the code and advise whether the feature is accepted or not?

Here is the PR: https://bitbucket.org/xi/libyaml/pull-request/5/add-block-and-flow-styles-for-sets-maps/diff