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.
http://dean.edwards.name/moz-behaviors/

Included CSS style:

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

Inline CSS style:

<p style="behavior:url(hilite.htc)">Hello World</p>

Apache MIME Type:

AddType text/x-component .htc

REFERENCES: