n is optional and specifies the number of average width characters in the
displayed output. Only values in range can be entered (see %co - Options for Edit). The range can
be set using %fl - Float Limit. Values are entered in decimal or exponent form.
If %`rf is specified, then the value presented can only be changed by the
program using window_update@(value).
grey_ctrl is 1 (enabled) or 0 (disable/greyed). A call-back function (if
present) is placed after this control variable.
option can be set to the keyword initially_blank in order to create an
edit box that is initially empty (see notes below).
The standard call-back functions 'COPY', 'CUT', and 'PASTE' can be used in this
context by attaching them to menu items and/or accelerator keys.
When %df - Spin for Float is used before %rf, a spin wheel is added (see %df - Spin for Float for details).
The subroutine set_highlighted@ can be called to select all of the text in
the edit box. It takes one argument which is the handle given by %lc - Handle of Last Control.