the "threads" normally referred to in the manual aren't OS threads, they're VM threads:  http://www.autohotkey.com/forum/viewtopic.php?p=155208#155208

g_nThread
g_nPausedThreads
g_MainThreadID
g_MaxThreadsTotal
g_nLayersNeedingTimer

struct global_struct  (aka "g"...  all thread-specific state data)

InitNewThread()
ResumeUnderlyingThread()



main loop is MsgSleep()'s for(;;)
    g_DeferMessagesForUnderlyingPump

somewhat related:
    g_MenuIsVisible
    g_nMessageBoxes
    g_nInputBoxes
    g_nFileDialogs
    g_nFolderDialogs
    g_InputBox
    g_Progress
    g_SplashImage
    g_gui
    g_hWndToolTip
    g_MsgMonitor
    g_MsgMonitorCount