This hook seems not to get called if an editing conflict occurs.
I copypasted the code examples and it took me a while to realize it's "$editpage" not "$editPage" in the function header.. maybe that could be fixed?
There's no way to use $editPage->editFormPageTop to inject wikitext? It would make it easier to accomplish certain things, such as page existence detection (red/blue wikilinks). Tisane 23:28, 12 March 2010 (UTC)
Shouldn't it say &$editPage? Tisane 19:16, 25 May 2010 (UTC)
I've just modified the text to indicate that the second argument ($output) was added in MW 1.20, not 1.12 as previously claimed.
I'm not sure where the 1.12 reference came from, as it was added by Dantman, who was the person who actually committed the fix in revision 14b524c1185097e96aab258f678991d87c1ac118. However, I've just done a detailed check, and it appears the $output argument was actually added in 1.20.
Specifically, here is the file in the 1.19 branch, which doesn't have the argument. Annoyingly, the branches/tags for 1.20 have been inexplicably erased from the internet (or else, very well hidden) so I can't link to the equivalent file in 1.20, but I have checked the tag locally and the second argument is present.