Setting this to a non-negative value causes the cell renderer to enter "activity mode", where a block bounces back and forth to indicate that some progress is made, without specifying exactly how much.
Each increment of the property causes the block to move by a little bit.
To indicate that the activity has not started yet, set the property to zero. To indicate completion, set the property to %G_MAXINT.
The "text" property determines the label which will be drawn over the progress bar. Setting this property to %NULL causes the default label to be displayed. Setting this property to an empty string causes no label to be displayed.
The "text-xalign" property controls the horizontal alignment of the text in the progress bar. Valid values range from 0 (left) to 1 (right). Reserved for RTL layouts.
The "text-yalign" property controls the vertical alignment of the text in the progress bar. Valid values range from 0 (top) to 1 (bottom).
The "value" property determines the percentage to which the progress bar will be "filled in".
The "orientation" property controls the direction and growth direction of the progress bar (left-to-right, right-to-left, top-to-bottom or bottom-to-top).