The first three examples under Names, do not work, copy-pasted I get an error message indicating "Symantic error in the filter expression".

eg, leader:find("arthas") gets the error message

If I instead use leader==arthas this will work, but requires correct, full spelling of the name including realm.

You are right, the example was incomplete, a full working example is leader:find("arthas") ~= nil because the string.find function in Lua returns nil when the pattern was not found and the indices in the original string where this occurrence starts and ends if it was found. Documentation is also updated.