"Unexpected call to method or property access" when trying to create a style tag

problem.js

// Problem

var css = 'a.check-css { color: #f00; }';
var el  = document.createElement('style');
el.setAttribute('type', 'text/css');
el.appendChild(document.createTextNode(css)); // Unexpected call to method or property access.
document.getElementsByTagName('head')[0].appendChild(el);

solution.js

// Solution

var style = document.createElement('style');
style.setAttribute('type', 'text/css');

if (style.styleSheet) { // Internet Explorer only
    style.styleSheet.cssText = css;
} else {
    style.appendChild(document.createTextNode(css));
}

head.appendChild(style);

test.js

// Test

injectCss("a.css-check { color: #f00; }");

// Add a test A tag with class css-check
var el = this.document.createElement('a');
el.className = 'css-check';
this.document.getElementsByTagName('body')[0].appendChild(el);

// Check its computed style
var style;

if (el.currentStyle) {// Internet Explorer only
    style = el.currentStyle;
    assertEqual(style.color, '#f00');
} else {
    style = this.document.defaultView.getComputedStyle(el, null);
    assertEqual(style.color, 'rgb(255, 0, 0)');
}