I was wondering that in the weight painting mode, how can I set a specific weight for a certain group of vertices instead of painting it over them?
Ah, I was fooling around and found an answer.
- In the weight painting mode, use the Vertex selection masking for painting V
- Select wanted vertices for example with Circle select tool C
- Set the wanted weight from Tool Shelf T
- Weights -> Set Weight Shift+K
In addition, there's a useful addon for setting weight values: http://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts/Paint/Palettes