* Control of fallback mappings in conversions.
-* Review the decision to coerce binary strings to Unicode when used as array
- keys.
-
* Figure out generic approach to locale validation/fallback.
-* Relax requirement on mixing unicode/binary strings in parameters
- (zend_get_unified_string_type() callers and others)
-
* Constant registration/fetching should do identifier normalization.
* Make zend_u_str_case_fold() do only case-folding and nothing else. The