Adds the class denoted by qname to line.
You may check if a line has qname by calling gtksource.gutter_lines.GutterLines.hasQclass.
You can remove qname by calling gtksource.gutter_lines.GutterLines.removeQclass.
a line number starting from zero
a class name as a #GQuark
Adds the class denoted by qname to line.
You may check if a line has qname by calling gtksource.gutter_lines.GutterLines.hasQclass.
You can remove qname by calling gtksource.gutter_lines.GutterLines.removeQclass.