An edit box created using %eb provides a wide range of advanced text editing
features. See Edit box (%eb) for
N represents the width of the box in average characters. M represents
the depth which, if omitted, defaults to 1.
buffer is a character string for the text which must be terminated with
buff_size is the size of the buffer. A zero value may be supplied to
allow the edit box to allocate its own memory re-sizing as required (buffer
%eb will take a pivot (%pv - Pivot).
If the caret modifier (^) is used and the call-back function does not handle the
response to control keys such as Delete, Backspace, etc., then it should return
a zero value.