Emitter (PyYaml, libyaml) settings so output is diff-friendly

I'm inspired by [1] to resume investigating an old goal: YAML data storage
in a version-control system, mainly for python programs.

I'd like to emit YAML that will always be zero-diff for equal data,
regardless of the circumstances under which the data was loaded.

Q: Is that considered indempotence? If not, what is the term for it?

Q: What parts of YAML 1.2 syntax would need to be constrained by the
Emitter to achieve this? Obvious to me are:

 - ordering of mapping keys, without emitting an omap
 - a default format for folded scalar text
 - default date and other scalar formats

But hopefully there is a way to know the complete set of all YAML syntax
that can be emitted non-(answer-to-the-previous-question)ly.

I would plan to choose preferences for those parts of syntax
per storage, and only expect zero-diff when comparing YAML emitted with
the same configuration (but not necessarily the same emitter library).

Perhaps constrained-syntax configurations would be useful in many YAML
projects.

And a question mainly for Kirill: 

Q: Does PyYaml and/or libyaml have configuration parameters for things
like this? Could they be put on the roadmap for new features, once I know
what they are and what to call them?


Thanks,
Jeff


[1] Using Git as a versioned data store in Python
http://www.newartisans.com/blog_files/git.versioned.data.store.php


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