https://www.zabbix.com/documentation/current/en/manual/config/triggers/prediction has:

timeleft(/host/vfs.fs.size[/,free],1h,0)}<1h

This is likely a leftover from the older syntax. Most likely multiple documentation versions are affected.

Somewhat related - https://www.zabbix.com/documentation/current/en/manual/appendix/functions/prediction calls them “prediction functions”, https://www.zabbix.com/documentation/current/en/manual/config/triggers/prediction - predictive. Might be worth unifying. The latter seems better, but worth checking with an expert in English.