It would be great for the polygon symbolizer interface to auto generate and
select the a new blank style layer when building opposite styles. This will make
it more intuitive for the user and will prevent the user from overwriting or
losing layer styles definitions.

For example:
- If the style layer has blank information 
  - Then builds a style in either the fill/stroke interface.
  - Then applies the fill/stroke style to this blank style layer. 
- That if the user selects the opposite symbolizing interface to begin building
a new style eg. fill to stroke or stroke to fill. 
  - Builds this opposite style 
  - Then applies the opposite style to the same style layer. 

Assuming: That the user has not in the meantime selected or added other style
layers.

Action: The expected action should be this opposite applied style will create a
new style layer and would be placed on top of the selected populated style layer
or on the bottom. Meaning on top of a fill style layer or bottom for stroke
style layer. This should also finally up date the overlaying preview (top left
image). The result of this preview should have a colored polygon with an outline.

Sorry for the complicated example.... if you have any question just ask me in
person. Thanks