(True for all parameters except wallpaper, POTY and POTD.)
If 1 is a valid parameter, 2 is always valid too. The same is true for 3 and 4.
For XXwiki parameters there is an additional parameter XXwiki-nom that can provide the nomination page (if it doesn't follow the standard scheme. For instance, enwiki-nom=Wikipedia:Feature picture candidates/Nomination name
A simpler method is to use subpage for commons, or enwiki-nom for English wikipedia. Format:
enwiki-nom=Bar.jpg [Links to Commons:Featured picture candidates/File:Bar.jpg or Commons:Featured picture candidates/Image:Bar.jpg]
enwiki-nom=Nomination name [Links to Wikipedia:Featured picture candidates/Nomination name (on the English Wikipedia)]
com-nom works similarly to XXwiki-nom, but has some very specific restrictions. It will ONLY work for nominations whose pagenames begin one of "Commons:Featured picture candidates/Image:", "Commons:Featured picture candidates/File:", or, for set nominations, "Commons:Featured picture candidates/Set:". If the nomination does not fit one of these patterns, it should be moved to the standardised location.
For nominations of the format:
Use com-nom this way:
Commons:Featured picture candidates/Image:Foobar.jpg or
Commons:Featured picture candidates/File:Foobar.jpg
Commons:Featured picture candidates/Set/Foobar or
Commons:Featured picture candidates/Set/Foobar
Move the nomination page so it fits one of the patterns listed above.