@Alias(existingAlias [parameter])

This returns the results of executing the alias as text. In effect this allows you to make custom procedures by making an alias containing script to return some text and using @alias(yourAlias) to invoke it.

For example given you could create an alias

/alias {proper %0}{@Upper(@Left($0),1)@Lower(@Right($0),@Math(@Len($0)-1)))}{MyAliases}

and then use it like @alias(proper mIXedCasE) and it would return
Mixedcase.