**Problem**
`Special:SetAliases` page does not allow the user to enter an alias that contains a `|` character in it's text. This is because the current page has only one field that instructs the user to enter the list of aliases, and split them with a `|` character.
Since a `|` character might have legitimate use-cases, being part of the alias text, such as in the following:
* https://www.wikidata.org/wiki/Q1161179 "Mac|Life"
* https://www.wikidata.org/wiki/Q1753348 "M|A|R|R|S"
we have to find a way to allow the user to use `|`s in aliases when they edit them through `Special:SetAliases` page.
**Suggested Solutions**
* make `Special:SetAliases` fail when there's already one or more alias on the item that contain a `|`. This can be done anyway as first iteration, then followed up by one of the following.
* provide the user with a sensible way to continue splitting aliases using `|`s, but to escape those that must be part of the alias text. (for example, they can escape a pipe by a pipe `||` or a backslash `\|`)
* use the TagMultiselectWidget from OOUI: https://doc.wikimedia.org/oojs-ui/master/demos/?page=widgets&theme=wikimediaui&direction=ltr&platform=desktop. (note: that does not work without JavaScript)
* add a new special page `Special:AddAlias` that adds one alias at a time (can have "add another" checkbox to redirect to it again).