How to use the rework.extend function in rework

css_code += css_part.toString();
        });

        var css = rework(css_code);
        css.use(svg(path.dirname(target)));
        if (rework_flags.autoprefixer) {
          css.use(autoprefixer(rework_flags.autoprefixer).rework);
        }
        if (rework_flags.at2x) {
          css.use(rework.at2x());
        }
        if (rework_flags.colors) {
          css.use(rework.colors());
        }
        if (rework_flags.extend) {
          css.use(rework.extend());
        }
        if (rework_flags.ease) {
          css.use(rework.ease());
        }
        if (rework_flags.references) {
          css.use(rework.references());
        }

        var css_result = css.toString({
          compress: minify
        });

        fs.writeFile(target_filename, css_result, callback);
      };

Style.prototype.toString = function(){
  this.use(rework.mixin(mixins));
  this.use(rework.keyframes());
  this.use(rework.ease());
  this.use(rework.prefixValue('linear-gradient'));
  this.use(rework.prefixValue('radial-gradient'));
  this.use(rework.prefixValue('transform'));
  this.use(rework.prefix(props));
  this.use(rework.colors());
  this.use(rework.references());
  this.use(rework.at2x());
  this.use(rework.extend());
  return this.rework.toString({ compress: this.compress });
};

#!/usr/bin/env node

var rework = require('rework');
var vars = require('rework-vars')();
var extend = require('rework').extend();
var ruleBinding = require('rework-rule-binding');
var autoprefixer = require('autoprefixer');
var program = require('commander');
var pkg = require('./package.json');
var stdin = require('stdin');

program.version(pkg.version).parse(process.argv);

stdin(function(str) {
  var options = {};
  var pre = rework(str).use(ruleBinding);
  var check = 0;

  pre.obj.stylesheet.rules.forEach(function(rule) {
    rule.declarations.forEach(function(declaration) {
      if (declaration.property.match(/^(inherit|extend)s?$/i)) {

Style.prototype.toString = function(){
  this.use(rework.mixin(mixins));
  this.use(rework.keyframes());
  this.use(rework.ease());
  this.use(rework.prefixValue('linear-gradient'));
  this.use(rework.prefixValue('radial-gradient'));
  this.use(rework.prefixValue('transform'));
  this.use(rework.prefix(props));
  this.use(rework.colors());
  this.use(rework.references());
  this.use(rework.at2x());
  this.use(rework.extend());
  return this.rework.toString({ compress: this.compress });
};