How Mysql full text search relevances compute?

How does MySQL compute the relevance of results of a full-text search? I know as it's documented:

Relevance is computed based on the number of words in the row, the number of unique words in that row, the total number of words in the collection, and the number of documents (rows) that contain a particular word.

But how these paramete开发者_JAVA百科rs come into those numbers?

Here there's the explain of the full-text algorithm http://forge.mysql.com/wiki/MySQL_Internals_Algorithms#Full-text_Search