Set the desired width of the status bar item. This can be either an absolute value in device-independent pixels
for a fixed width field or a negative value indicating a proportion for a variable
width field. The space left for all variable width fields is divided between them according to
the absolute value of this number. A variable width field with width of -2 gets twice as
much of it as a field with width -1 and so on.
For example, to create one fixed width field of width 100 in the right part of the status bar
and two more fields which get 66% and 33% of the remaining space correspondingly, you would
set the width fields of the items to -2, -1 and 100, respectively.
Defaults to -1.