[css-transforms-1] How precise can we be about serialization?

So as part of some tests I'm writing, I'm using transform: rotate(90deg); and testing the serialization. As specified, at computed/used time this becomes a matrix(); no problem.

However! In Firefox, a 90deg rotation like that produces the nice, simple serialization of matrix(0, 1, -1, 0, 0, 0). In Chrome, it instead gives matrix(6.12323e-17, 1, -1, 6.12323e-17, 0, 0), aka two of the zeros are instead incredibly small non-zero values.

These two matrixes don't produce a rendering difference, but it sure makes it difficult to test serialization. How precisely do we want to specify this kind of thing? How do browsers test their own serialization in the face of issues like this?

No files or tests are named. Start by reading the CSS Transforms 1 serialization rules and the reported Firefox and Chrome outputs, then determine whether the specification should define precision or canonicalize near-zero matrix values. Done means a clear specification decision and corresponding guidance for serialization tests.