I just gained the "Edit Tag Wikis" privilege and went to edit the
z-index tag. It "has no wiki" and I would like to help create it, so I clicked the link.
You may have broken the level of 1500 EXP, but for that particular tag you have neither
- a bronze badge for calls to sharecropping duty
- a spot in the top 20 answerers of all time OF ALL TIME!
Since you fail on both counts, you can rule yourself out of being able to edit the tag wiki at this stage.
The new edit suggestion system allows you to suggest edits or new wikis for any tag.