* unicode in `..`?

* EBCDIC support?

* Discuss putting ZEND_ATTRIBUTE_FORMAT back on zend_error() or create a new
  zend_error_ex() function that supports new specifiers

* Determine how to deal with filesystem and filenames when Unicode is
  involved. This concerns both the extension functions and things like
  compile_file(), open_file_for_scanning(), etc.

* Measure performance difference when doing quickCheck + normalize versus
  simple normalize.

* Find all instances where unicode strings are compared with memcmp() and
  replace either with u_memcmpCodePointOrder() or ucol_strcoll()

* Opening a collator may return U_USING_DEFAULT_WARNING,
  U_USING_FALLBACK_WARNING

* Need to finish making HTTP input work as described in the design doc. It
  is almost there, but needs to handle conversion errors and provide a way to
  explicitly re-decode raw data with specified encoding. Also check for
  _charset_ request field which might be present.

* Optimize T_INLINE_HTML blocks conversion by either creating a converter
  cache or remembering the last used converter in the executor globals.

* What to do with binary string literals and runtime casting? Literals are in
  script_encoding, casting uses runtime_encoding. If they are different, bad
  stuff happens.

* Control of fallback mappings in conversions.

* Introduce ability to request strings in a specific encoding in parameter
parsing API, e.g.:

    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s(ASCII)",
            &locale, &locale_len) == FAILURE) {
    }

* 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.

* Identifier normalization in callbacks (zend_is_callable/zend_u_lookup_class)

* Make zend_u_str_case_fold() do only case-folding and nothing else. The
  normalization should be done by zend_normalize_identifier().

* Look at performance implications of identifier normalization.