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Next release:
    - backbuffer="true|false|mask|filter"
    - filters (filtering of a group must be performed AFTER the group is assembled)
    - arbitrary alpha channeling
    - DirtyRegion needs to use microtile arrays

    - need svg.xwt
       - need sax-in-template
       - text-along-a-path using readback from path attribute
       - non-hairline lines as stroke-to-fill conversion
           - includes mitre, bevel, and bump joins
       - dashed lines as intermediate conversion
                                                                                                                                    
    v1.1                                                                                                                            
    - subtree sharing? otherwise the memory consumption might be outrageous... clone="" attribute?                                  
    - faster gradients and patterns:                                                                                                
        - transform each corner of the trapezoid and then interpolate     
    - bilinear transforms?