On https://www.zabbix.com/documentation/2.2/manual/appendix/items/supported_by_platform we defined that - "Parameters that are included in angle brackets <like_this> are optional."
Of course this page talks only about agent items, but...

For example consider https://www.zabbix.com/documentation/2.2/manual/config/items/itemtypes/internal
There are two keys:
zabbix[java,,<param>]
zabbix[queue,<from>,<to>]

They look similarly, yes?
But for zabbix[java,,<param>] key 3rd parameter is required when in the same time for zabbix[queue,<from>,<to>] 2nd,3rd parameters are optional.

In frontend item key selection helper provides these suggestions:
zabbix[java,,<param>] Returns information associated with Zabbix Java gateway. Valid params are: ping, version.
zabbix[queue,<from>,<to>] Number of items in the queue which are delayed by from to to seconds, inclusive.

This inconsistency sometime complicated zabbix usage w/o looking to documentation periodically.
Would be nice to improve it somehow, not sure how exactly.
Solution should be unified for documentation and frontend.