[climech]

I believe something like this would work (excuse the comments normally not allowed in JSON):

    {
      paths: [
        {
          points: [
            [10, 10],  // 0
            [90, 10],  // 1
            [90, 90],  // 2
            [10, 90]   // 3
          ],
          lines: [
            [0, 1, 2, 3, 0]  // connect point 0 to 1 to 2 to (...)
          ],
          curves: {
            0: [5, 15, 15, 5]  // bezier control points for point 0 (x1, y1, x2, y2)
          }
        }
      ]
    }

The downside (other than the bloat) would be when writing the code by hand, you'd have to keep track of the indices in the `points` array.

[jcelerier]

i'd much rather have

    [ { line: [10, 10] }, { cubic: [ 5, 15, 15, 5 ] }, ... ] 

or even

    [ ["line", 10, 10], ["cubic", ...], ... ] 

- anything as long as there's a way to stream the data (which is not possible with your format as you need to receive the whole object before being able to do anything).

[afiori]

this makes me realize that xml maps relatively well to JSON array whose elements are object with 1 fields (or 2 fields) whose value is again a similar array.