points towards Solr 4.x wiki
The moinmoin wiki is not for 4.x. A lot of the content has gotten out of date, but other parts of it are updated regularly and have fully current information.
That older wiki needs an overhaul. Some of the information needs to be removed because the information in the reference guide is better and completely supersedes what's there now, but there is still some value in having duplicate information for certain topics, because the wiki version can be presented differently, in a format that's better for quick lookups than the reference guide, which is intended to be full documentation. A good example of this is the following page:
I use this page all the time, because it's easily searchable for a particular analysis component and has quick-n-dirty examples. I don't recall seeing anything in the reference guide like that page.