My current idea is that the Unicode-related functions should be documented separately from the i18n functions. Your list doesn't seem complete, though: where is unicode-encode.xml ?
In any case, from that list, everything starting with collator* or locale* should be in i18n section and the rest - in Unicode section.
We also need a top-level section where we give intro to Unicode, how it works in PHP, new string types, operators, etc.
Using scripts/xml_proto.php generates 86 functions from php-src/ext/unicode/, a generated [proposed categorized] list is appended to this email.
The Doc Unicode RFC states having a features/unicode section too:
http://doc.php.net/php/rfc/rfc-proposal-show.php?id=6
That seems like a good place for the top-level section you desire. Basically:
reference/unicode/reference.xml (geared towards the extension)
features/unicode.xml (talks all about Unicode in PHP 6+)
If additions/changes are needed to that RFC, now is a good time for us to discuss them as it's been approved as is. Here's that complete list generated from php-src/ext/unicode/, and likely categorized as you suggest. If it looks good we can add the skeletons now including one for the new Unicode features page. Here goes:
--
ref.i18n
--
collator_compare()
collator_create()
collator_get_attribute()
collator_get_default()
collator_get_strength()
collator_getattribute()
collator_getstrength()
collator_set_attribute()
collator_set_default()
collator_set_strength()
collator_setattribute()
collator_setstrength()
collator_sort()
locale_get_default() (rename/move i18n_loc_get_default() from current docs)
locale_set_default() (rename/move i18n_loc_set_default() from current docs)
--
ref.unicode
--
char_enum_names()
char_enum_types()
char_from_digit()
char_from_name()
char_get_age()
char_get_combining_class()
char_get_digit_value()
char_get_direction()
char_get_mirrored()
char_get_name()
char_get_numeric_value()
char_get_property_from_name()
char_get_property_max_value()
char_get_property_min_value()
char_get_property_name()
char_get_property_value_from_name()
char_get_property_value_name()
char_get_property_value()
char_get_type()
char_has_binary_property()
char_is_alnum()
char_is_alpha()
char_is_alphabetic()
char_is_base()
char_is_blank()
char_is_cntrl()
char_is_defined()
char_is_digit()
char_is_graph()
char_is_id_ignorable()
char_is_id_part()
char_is_id_start()
char_is_iso_control()
char_is_lower()
char_is_lowercase()
char_is_mirrored()
char_is_print()
char_is_punct()
char_is_space()
char_is_titlecase()
char_is_upper()
char_is_uppercase()
char_is_valid()
char_is_whitespace()
char_is_xdigit()
str_transliterate()
textiterator_construct()
textiterator_current()
textiterator_first()
textiterator_following()
textiterator_getall()
textiterator_getavailablelocales()
textiterator_getrulestatus()
textiterator_getrulestatusarray()
textiterator_isboundary()
textiterator_key()
textiterator_last()
textiterator_next()
textiterator_offset()
textiterator_preceding()
textiterator_previous()
textiterator_valid()
unicode_decode()
unicode_encode()
unicode_get_error_mode()
unicode_get_subst_char()
unicode_restore_error_handler()
unicode_semantics()
unicode_set_error_handler()
unicode_set_error_mode()
unicode_set_subst_char()