Sometimes, it is not quite clear why a query matches a given search string. To debug your query, PostgreSQL offers the ts_debug function. From a user's point of view, it can be used just like to_tsvector. It reveals a lot about the inner workings of the FTS infrastructure:
test=# \x
Expanded display is on. test=# SELECT * FROM ts_debug('english', 'go to www.postgresql-support.de'); -[ RECORD 1 ]+---------------------------- alias | asciiword
description | Word, all ASCII
token | go
dictionaries | {english_stem} dictionary | english_stem lexemes | {go}
-[ RECORD 2 ]+---------------------------- alias | blank
description | Space symbols token |
dictionaries | {} dictionary | lexemes | -[ RECORD 3 ]+---------------------------- ...
