Meta function automatically created by thinBasic engine and valid only inside Callback Functions.
nmHDR = CBNMHDR
nmHDR = Callback_Notify_Address
Some notification messages like %NM_CHAR, %NM_CLICK, etc. require an extended version of the NM structure. However, all NM structures begin with an NMHDR UDT, so the pointer returned here is always accurate. For other values of CBMSG, the pointer returned by CBNMHDR is meaningless.
This function is only valid inside a Callback Function.