$world->aliasenabled
This functions checks whether the specified alias exists and whether it is enabled.
You can pass either a alias number or name. If the alias does not exist, this function returns undef, so you can distinguish the case of a non-existant alias from a disabled one.
If the alias exists, then the function returns 0 or 1 depending on whether it is enabled or not. If you pass a name, and there are several aliases with the same name, it returns a list with one value for each alias with that name, and each value is 0 or 1 depending on the state of the alias.