At the moment the WRONG text "groupOutput" counted 15 times in 1.8 doc, and 12 times in 2.0 doc.
The CORRECT text "groupCount" counted 0 times in 1.8 doc, and 5 times in 2.0 doc.
Documented parameter "groupOutput" is wrong, it's some mistake, it appeared in documentation first time here http://www.zabbix.com/documentation/1.8/api/host/get
2010/08/05 14:41 1.8:api:host:get - aly
Why 2.0 API doc has less errors and has 5 correct parameters? -> because those 5 places fixed by Pavel recently as partial review 2012/05/18 14:26.
During the review groupOutput have been changed to groupCount on 5 pages.
Actually 1.8 API doc pages have many copy-paste mistakes and they all come (I have some reasons to suppose this) from host.get method. Probably it was a "base" method to create documentation and perform changes in sources.
In a revision 10593 an outdated parameter "count" has been changed to "countOutput" AND new parameter "groupCount" (at least for method get() of classes: host, item, graph, application, template, trigger) has been added.
It happened 2010/03/04 - a long lime before (~ 5 months) creation API documentation.
So, my conclusion is that "groupOutput" it's just a old MISTAKE, which later populated across all documentation.
The parameter "groupOutput" exists only in one place - for the history.get method (together with "groupCount"), it's true for 2.0 and 1.8 sources and it's ok.