fix export-area description

(cherry picked from commit c1f57e76)

man/inkscape.pod.in

@@ -226,14 +226,14 @@ it can be used in combination with L<--export-use-hints>.
 
 =item B<-a> I<x0:y0:x1:y1>, B<--export-area>=I<x0:y0:x1:y1>
 
-In PNG export, set the exported area in SVG user units (anonymous length
-units normally used in Inkscape SVG).  The default is to export the
-entire document page.  The point (0,0) is the lower-left corner.
+In PNG export, set the exported area of the document, specified in px 
+(1/96 in). The default is to export the entire document page. The point 
+(0,0) is the lower-left corner.
 
 =item B<--export-area-snap>
 
-For PNG export, snap the export area outwards to the nearest integer SVG
-user unit (px) values. If you are using the default export resolution of
+For PNG export, snap the export area outwards to the nearest integer px 
+values. If you are using the default export resolution of
 96 dpi and your graphics are pixel-snapped to minimize antialiasing,
 this switch allows you to preserve this alignment even if you are
 exporting some object's bounding box (with L<--export-id>