1. Regarding an "Alias" parameter a page:
https://www.zabbix.com/documentation/2.0/manual/appendix/config/zabbix_agentd
doesn't have clear description and example for the parameter.
since this page:
https://www.zabbix.com/documentation/2.0/manual/appendix/config/zabbix_agentd_win
is much better.

Need to extend *nix page and review windows' one. For example this sentence looks complicated:

Aliases cannot be used for parameters defined in "PerfCounter" configuration file records.

I think it could be:
"Aliases cannot be reused in "PerfCounter" parameters."

Description also should provide a hint that it allows to create several items in zabbix frontend with different custom keys, which will return identical value from agent.
Might be single workaround in case: need several LLD rules with identical keys but with different filters.

2. Default zabbix_agentd.conf must have the parameter syntax example. Also need to mention that multiple aliases are allowed.

3. For both 1 and 2: why we say "Sets an alias for parameter" ?
Why not "Sets an alias for item key" ?
Which would be more correct! IMO.