Character string input format - %nrs
This format takes one character variable and displays it in a single line edit
box so that the user can change it. Optionally, it can be modified with an
integer n that sets the width of the box in characters. The edit box
will then scroll horizontally when necessary. For multiple line edit boxes see
%re (%re - Multiline Edit Box) and %eb (Edit
str='Initial string padded with spaces if needed'
It is important to note that because there is an obvious difference between the
widths of characters e.g. 'i' and 'W', the width is specified in 'average
A grave accent format modifier (`) is used to make the control read-only. In
this form no surrounding box is displayed, and the string can only be changed
by the program, using window_update@ to reflect the changes. This should
be used in place of %ws when it is necessary to display a string which needs to
be updated. A similar effect is produced with %st. (see
Variable string). The caret is added to provide a call-back function
that will be called on every change to the edit window.