Via Special:Block, users with oversight permissions (and the `hideuser` right) can configure a block to both prevent a user from editing ("block") and scrub the UI of their username ("suppress"). On Test Wiki this is limited to only indefinite blocks, but it may be different across our various wikis.
Suppression is only appropriate for sitewide blocks. **Defect:** The Sp:Block UI allows an oversighter to suppress a user for a partial block.
* For users with the `hideuser` right...
** On Special:Block, the "Hide username from edits and lists" checkbox should only appear if the radio button is set to "Sitewide"
** If the person changes a suppressed sitewide block to a partial block, it should become unsuppressed.
** API submissions to suppress for partial blocks should return an appropriate error message