Why I can index text field use Btree?

Question

When I read the document https://mariadb.com/kb/en/text/#indexing I see that: "TEXT columns can only be indexed over a specified length;..; Internally, this uses hash indexing to quickly check the values and if a hash collision is found, the actual stored values are compared in order to retain the uniqueness.". But when I trying to create an index by query: CREATE INDEX content_text_IDX USING BTREE ON content (field_text); I still can create btree index without specifying any length.