text: "use strict";
  
  
  var ___inserted = [];
  
  function injectCss (css, id) {
    var domStyle = document.createElement("style");
    domStyle.id = id;
    domStyle.textContent = css;
    document.head.insertBefore(domStyle, document.head.firstChild);
  }
  
  /**
   * Inject the css string into the <head> tag within a <style> tag. If once is set to true,
   * the css matching this ID will only be injected once 
   * 
   * @param {string} css the css that will be injected into the style
   * @param {string} id the ID value of the style tag, should be unique
   * @param {?boolean} once if the css matching the ID can only be injected once (=true)
   */
  function cssToHead (css, id, once) {
    if (once === undefined) once = true;
    if (once) {
      if (___inserted.indexOf(id) === -1) {
        injectCss(css, id);
        ___inserted.push(id);
      }
    } else {
      injectCss(css, id);
      ___inserted.push(id);
    }
  }
  
  module.exports = cssToHead;