followed by example doesn't work

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/9.6/static/textsearch-intro.html
Description:

I copied the text in the followed by example: SELECT to_tsvector('fatal
error') @@ to_tsquery('fatal <-> error');
but it will always goes in error: ERROR: syntax error in tsquery: "fatal
<-> error"
SQL state: 42601
I find two ways to solve the problem:
1. remove the space inside the to_tsquery string to obtain 'fatal<->error'
2. use plainto_tsquery instead of to_tsquery.