in the future. Some unusual cases such as fictional languages are outside the usual scope of Unicode but not explicitly ruled out by the principles of Unicode, and may show up eventually (such as the Star Trek and Tolkien writing systems). In other cases, the proposed encoding violates one or more Unicode principles and hence is unlikely to ever be officially recognized by Unicode—mostly where users want to directly encode alternate forms, ligatures, or base-character-plus-diacritic combinations (such as the TUNE scheme). Emoji is an encoding for picture characters or emoticons used in Japanese wireless messages and webpages. With Unicode 6.0 and later, many of these have been encoded in the block Miscellaneous Symbols And Pictographs and elsewhere in the SMP. GB/T 20542-2006 ("Tibetan Coded Character Set Extension A") and GB/T 22238-2008 ("Tibetan Coded Character Set Extension B") are Chinese national standards that use the PUA to encode precomposed Tibetan ligatures. GB 18030 and GBK use the PUA to provisionally encode characters not found in Unicode standards at the time of publication (most have been encoded since then). The Institute of the Estonian Language uses the PUA to encode Latin and Cyrillic precomposed characters that have no Unicode encoding. The Free Tengwar Font Project uses a different mapping from the ConScript Unicode Registry that largely follows Michael Everson's 2001-03-07 Tengwar discussion paper, but diverges in some details. The MARC 21 standard uses the PUA to encode East Asian characters present in MARC-8 that have no Unicode encoding. The SIL Corporate PUA uses the PUA to encode characters used in minority languages that have not yet been accepted into Unicode. The STIX Fonts project uses the PUA to provide a comprehensive font set of mathematical symbols and alphabets, many of which are also available in the SMP now, e.g. in the Mathematical Alphanumeric Symbols block. The Tamil Unicode New Encoding (TUNE) is a proposed scheme for encoding Tamil that overcomes perceived deficiencies in the current Unicode encoding. Vendor use Informally, the range U+F000 through U+F8FF is known as the Corporate Use Area. This originates from early versions of Unicode, which defined an "End User Zone" extending from U+E000 upward and a "Corporate Use Zone" extending from U+F8FF downward, with the boundary between the two left undefined. The Adobe Glyph List used to use the PUA for some of its glyphs. Apple lists a range of 1,280 characters in its developer documentation from