HTC/.htc files

What is it? Internet Explorer 5-9 introduced behaviors. Behaviors are a way to add behaviors to XML (or HTML) elements with the use of CSS styles.

Why avoid it? The behavior attribute is only supported by Internet Explorer.

What to use instead? Use JavaScript and XML DOM (or HTML DOM) instead

MSIE 5-9 support a scripting (VBScript/JScript) technology called HTML Components (HTCs) to aid in DHTML behaviors. Support was dropped in MSIE 10, you will have to force the browser into MSIE 9 compatibility to use these.

Mozilla? it has a similar proprietary implementation.

Included CSS style:

<style type="text/css">
h1 { behavior: url( }

Inline CSS style:

<p style="behavior:url(">Hello World</p>

Apache MIME Type:

AddType text/x-component .htc


Avoid CSS Expressions

MSIE5 added support for CSS expressions or “Dynamic Properties”, however MSIE8 ‘deprecated’ their use and prevents their use in Standards Mode.

While powerful because this allowed you to script your CSS dynamically, there were two primary problems.

  1. Performance – the expression could fire literally hundreds or thousands of times on a page when scrolled or resized.
  2. Security – this represented an attack vector and exposed XSS


Dynamic HTML style tag with JavaScript

I recently got into some heavy refactoring of legacy code and in an effort to “fix” some JavaScript that was directly manipulating ‘style’ attributes on a DOM element and thus introducing maintenance and specificity issues I found that it would be “easier” to add a CSS class that I would write dynamically… leading to many headaches along the way and this bit of knowledge.

“For MSIE, you cannot simply write a ‘textNode’ into the DOM for HTML STYLE tags, you must use ‘cssText'”

function createClass(cls,txt){
var obj = document.createElement('style');
var head = document.getElementsByTagName('head')[0];
var val = '.' + cls + '{' + txt + '}';
var nod = document.createTextNode(val);
if(obj.styleSheet){// MSIE
obj.styleSheet.cssText = nod.nodeValue;
} else {