* 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

* Should we apply identifier validity checks in functions that deal with
  identifiers, such as define(), get_class(), etc?

* Resolve the differences in %G output format. sprintf() removes trailing
  zeroes from the fractional part, and u_sprintf() doesn't.

* 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.

* output.c needs a lot of work as it passes char* around

* 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.