code: function installPeerDeps() {
  
    // check for the "kill switch"
    if (process.env[envLabel]) {
      console.log('Skipping installing peerDependencies as devDependencies.');
      return;
    }
  
    // yo, do not install peers while installing peers
    process.env[envLabel] = '1';
  
    getPackageConfig(rootPath, function(config) {
      var peerDeps           = getPeerDeps(config)
        , peerInstallOptions = getPeerInstallOptions(config)
        ;
  
      if (!peerDeps) {
        console.error('Unable to find peerDependencies in ' + rootPath);
        return;
      }
  
      // ready to install, switch directories
      process.chdir(rootPath);
  
      // TODO: Add more alternatives
      // TODO: Handle `peerInstallOptions` for npm and yarn
      if (installYarn) {
        installYarn(peerDeps, peerInstallOptions, installDone.bind(null, 'yarn'));
      } else if (installNpm) {
        installNpm(peerDeps, peerInstallOptions, installDone.bind(null, 'npm'));
      } else {
        console.error('Did not find a viable package manager to install dependencies with.');
      }
    });
  }
docs: --- Subroutines