The spec appears to be quite clear, the user may also escape the unbalanced parenthesis
[link](https://www.depotlegal.be/Depot/form.aspx?SC=KBRVITRINE1#/Search/\(query:\(AdvancedQuery:\(queryGroups:!\(\(queryClauses:!\(\(index:KBR264b_idx,logical:0,operator:0,otherValue:!n,value:'petites%20singularit%C3%A9s'\))
becomes
Since this is working as described in the spec I’m moving it to Feature discussion.