Pure PHP implementation, so you don't need to make any modifications to the server for installation. If speed is of dire concern, it might not be the ideal solution, but if you're using YAML for configurations or relatively low-volume use, it is a fantastic solution.
Given a YAML document, Spyc will return an array that you can use however you see fit.
If you're using a lot of YAML in your project you may find that the pure PHP libraries like spyc or Symfony YAML are not fast enough. There are at least two PHP bindings for C YAML parsers:
yaml - a wrapper for the LibYAML YAML 1.1 parser library
syck - a wrapper for the Syck YAML 1.0 parser library
syck: Binding to syck; also available as a PECL extension. (dated, see below)
Pure PHP implementations:
sfYaml: Symfony's YAML component. You can see its authors' motivations here. He wanted something that was "easy to use, fast, unit tested and had clear error messages."
At the time of this writing, the latest versions release dates for the aforementioned libraries and the versions of the YAML spec (1.2 is the latest version) they support are: