Many, many plugins provide shortcodes. The oik shortcode help facility will list all the “active” shortcodes. If it doesn’t know anything about them then it will display the shortcode name followed by a question mark. e.g. [youtube] – ?
Under this page you might find a summary of shortcodes we’ve been asked about. e.g. [[youtube]]
[[youtube]] video shortcode from Jetpack
and without any anchor tags ( <a href=blah… )
see for yourself…
hover to slideToggle source