Example metadata.json with compatibility expressions

metadata.json

{
  "requirements": [
      { "name": "pe", "version_requirement": "3.x" },
      { "name": "puppet", "version_requirement": "3.x" }
    ],
  "operatingsystem_support": [
      {
        "operatingsystem": "RedHat",
        "operatingsystemrelease": [
          "5",
          "6"
        ]
      },
      {
        "operatingsystem": "CentOS",
        "operatingsystemrelease": [
          "5",
          "6"
        ]
      },
      {
        "operatingsystem": "Scientific",
        "operatingsystemrelease": [
          "5",
          "6"
        ]
      },
      {
        "operatingsystem": "Debian",
        "operatingsystemrelease": [
          "6",
          "7"
        ]
      },
      {
        "operatingsystem": "Ubuntu",
        "operatingsystemrelease": [
          "12.04"
        ]
      }
    ]
}

http://puppetlabs.com/blog/puppet-forge-search-module-compatibility has more