The interpertation of this function is dependent on the value of ulEffect. This function is considered "window related" when ulEffect is LI_BD_WND_ATTR or LI_BD_WND_STAT.
When ulEffect is not window related then the value of hwnd must be NULL.
On the other hand, when ulEffect is window related, the function optionally sends a WM_QUERYBIDIATTR or WM_QUERYBIDISTAT message to the window procedure whose information is being queried. The window procedure which is queried for bidi information can take some action and/or perform any additional processing that is required at this time. When LIF_NO_SENDMSG flag is specified no window message is sent by the function. This can be used by the window procedure itself when it queries its own window-related bidirectional information (so that it does not receive a recursive message).
It is recommended that the LIF_NO_SENDMSG flag is not turned on when the function is called from outside the window procedure whose attributes are being queried. Applications should generally use the default (send the message to the window procedure), so that the bidi aware window procedures can take the appropriate actions when the request to query their bidi attributes is made.