type

A string that describes the type of content being sent, such as:

• CommentType.COMMENT

• CommentType.FORUM_POST

• CommentType.REPLY

• CommentType.BLOG_POST

• CommentType.CONTACT_FORM

• CommentType.SIGNUP

• CommentType.MESSAGE

• CommentType.PINGBACK

• CommentType.TRACKBACK

• CommentType.TWEET

You may send a value not listed above if none of them accurately describe your content.

This is further explained here.