The help file says that passing an empty string to WVISIBLE() means that you are referring to the main Visual FoxPro window.

>>Go to the command window and type:
>>
>>CLOSE ALL
>>? WVISIBLE(ALIAS())
>>
>>It's returning TRUE for me
>>
>>Strange
>
>When there isn't a table open in the current workarea, ALIAS() returns "". My guess is if the NULL string is passed to the WINVISIBLE*( function, it uses the active window. The same behavior exists for WEXIST().