code: function (ctx, next) {
          var plugins = []
          var config = process.cssy.config
  
          ctx.imports = []
  
          var parseImportPlugin = postcss.plugin('cssy-parse-imports', function () {
            return function (styles) {
              styles.walkAtRules(function (atRule) {
                if (atRule.name !== 'import') {
                  return
                }
                if (/^url\(|:\/\//.test(atRule.params)) {
                  return // Absolute
                }
                ctx.imports.push(parseImport(atRule.params))
                atRule.remove()
              })
            }
          })
  
          if (ctx.config.import) {
            plugins.push(parseImportPlugin)
          }
  
          if (config.minify) {
            plugins.push(cssnano(extend({}, (typeof config.minify === 'object')
              ? config.minify : DEFAULT_MINIFY_OPTIONS)))
          }
          postcss(plugins)
            .process(ctx.src, {
              from: ctx.filename,
              to: ctx.filename + '.map',
              map: {
                prev: ctx.map,
                inline: config.sourcemap
              }
            })
            .then(function (result) {
              ctx.src = result.css
              if (config.sourcemap) {
                // TODO: Dig sourcemap, dig more.
                ctx.src += '\n/*# sourceURL=' + ctx.filename + '.output*/'
              }
              ctx.map = result.map
              next(null, ctx)
            })
  
          next(null, ctx)
        }
docs: 6. Extract importations and generate source