rel="help" attribute value specifies that the linked page contains context-sensitive help for the current page or the parent element of the link.
rel="help" on an href element.
This link opens context sensitive help.
The rel attribute defines the relationship between the current page and the linked page.
rel="help" value indicates that the link offers context-sensitive help for the current page.
It can also mean that the help is for the parent element of the link with
<tagname rel="help" />
These elements accept the help value on the rel attribute.
|<a>||Specifies an anchor link -- see example above|
|<area>||Creates clickable areas inside an image map.|
|<form>||Specifies an HTML form.|
|<link>||Links a resource to the current page|
Here is when rel support started for each browser: