We have the following known issue in ICU 4.6: A collation rule using the new star notation “<*” in which the list of characters following “<*” includes two successive APOSTROPHE characters ( ' ' ) is malformed, but may not be detected and will produce erroneous results.
So we need to detect this in ucol_openRules and the like. We may not need to check for this in genrb if LDML2ICUConverter is changed to never generate this.
Peter & Mark request that apostrophe be forbidden in `<` and similar if it comes from two consecutive apostrophes. (Because it's error-prone.) That is, one would instead have to use `\u0027` or stop the `<` and use `<''` or similar.
This works fine with the new collation code. I added a unit test case.