This issue was added by Oleg upon my request.
I'd like to clarify my point of view.
The documentation claims that the "logseverity" trigger function returns an "integer, useful for Windows event logs". However, when we are constructing the trigger expression, we need to know the exact values for comparison. Unfortunately, these values still undocumented. For me, for example, it was necessary to search using google; I found an examples on Zabbix forum only. Finally, the real full list of these values I found in the sources (file include/common.h, group of constants ITEM_LOGTYPE_*). It is absolutely unnecessary troubles and lost of my time: evidiently, these constants must be documented.
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Sincerely yours,
Constantin Oshmyan

P.S. NB! Real values returned by the "logseverity" trigger function look to be just as in this include file. It differs from the examples provided by Oleg!

Thanks Constantin, "logseverity" levels updated.

Documentation improved in https://www.zabbix.com/documentation/2.2/manual/appendix/triggers/functions

Thanks for reporting.

sasha Thanks! CLOSED