What is the maximum possible value range of MATCH ('...' IN NATURAL LANGUAGE MODE) in MySQL?

MySQL provides FULLTEXT indexes, that can be retrieved with the MATCH (col1,col2,...) AGAINST (expr [search_modifier]) construct. There are several Full-Text Search variants, one of them (and the default one) is the Natural Language Full-Text Search.

So what is the maximal possible value of the MATCH ('...' IN NATURAL LANGUAGE MODE)?

Example:

This query

SELECT
    courses.id,
    courses.title,
    MATCH (coursedata.title) AGAINST ('Basketball') AS relevance
FROM
    courses
JOIN
    coursedata ON coursedata.id = courses.coursedata_id
WHERE
    MATCH (coursedata.title) AGAINST ('Basketball') > 0

returns a result table with column relevance, where we're storing the relevance value of coursedata.title rows for 'Basketball'. Or the relevance value of 'Basketball' for coursedata.title rows? Anyway, we're storing there the output of the MATCH(...) function. In my case I'm geting values from 0 to 3.695953130722046.