From the help file with mIRC 6.21
edit "text", id, x y w h, style (right, center, multi, pass, read, return, hsbar, vsbar, autohs, autovs, limit N)
Where "text" is the default text for a control, id is a number that uniquely identifies a control, x y w h are the position and size of the control, and style consists of a combination of the words in brackets.
Other Styles
In addition to the styles shown in brackets for each type of control, you can also specify these styles:
disable disables the control
hide hides the control
group start of a group
result identifies the control whose value will be used as the return value to the calling script when the user presses the ok button
