General

WORDPRESS

WordPress.com can’t used these code.

HTML
you’ll notice that codes such as embed, frame, iframe, form, input, object, textarea and others are missing from the above list. Those codes are not allowed on WordPress.com for security reasons.
Javascript
Users are not allowed to post JavaScript on WordPress.com blogs. JavaScript can be used for malicious purposes.
Flash and Other Embeds
Flash and all other embeds are not allowed in WordPress.com posts, pages, or text widgets.
Plugins
Plugins are not allowed on blogs at WordPress.com for security reasons. Plugins are for self-hosted blogs using the software from wordpress.ORG.