don't follow the simplification algorithm so closely

[lddubeau]

Problem

Relax NG specifies that during simplification group, interleave and choice are transformed so that each of them contain at most two children. (That's step 10.) This leads to a multiplication of elements and some complications:

1. It takes time to perform the transformation.

2. More elements means more walking during later simplification steps and during constraint checks.

3. It also leads to a bigger JSON file once serialized.

4. It also means a deeper walker tree during validation, though this may not have that much impact on validation performance.

Solution 1: Don't Perform the Work in Step 10

Not performing the simplification of these elements would take care of the issues above. However:

• It requires rewriting Group, Interleave and Choice to handle multiple children, which may make them much more complex.

• It means losing the 1-to-1 steps between our internal simplifier and the old XSL code. Harder to test.

• We need to carefully assess the impact on later simplification steps because they assume that the transformation in step 10 has been done.

• It may also affect the constraint checks.

Solution 2: Add a Later Step Which Collapses the Elements

Another approach, rather than not performing the transformation, would be to add a step that would collapse the group, interleave and choice elements at the end of simplification. This would take care of complications 3 and 4 but it would add to the total simplification time.