For example, I can enter "895894791278749" and that will submit, leaving a blank item under "namespaces" in the Special:BlockList (see screenshot) and an entry of "2147483647" (largest integer allowed?) in the ipblocks_restrictions table.
You can also enter a value like 34783.47847 and that will block namespace 34783 (presumably it just rounds to nearest integer).
This did not appear to have any bad side-effects. The user is still blocked from pages they are partially blocked from and able to edit pages they are not blocked from.
The mediawiki instance will need to have: "$wgEnablePartialBlocks = true;"
- Go to Special:Block
- Type in a valid user (you won't get completion without JS)
- Select the "Partial" radio button
- In the "Namespaces" input type any positive number
- Choose an expiration (you need to type in a value, doesn't seem to matter)
You can see the settings of the block you have just set in Special:BlockList.