Karl Williamson noted: > The FAQ http://www.unicode.org/faq/private_use.html#sentinels > says that the last 2 code points on the planes except BMP were made > noncharacters in TUS 3.1. DerivedAge.txt gives 2.0 for these. >
The *concept* of noncharacter was not invented until Unicode 3.1, so it could not have formally been applied to anything before then. Before Unicode 3.1, some code points had been referred to as "not a character", but it took a while for the UTC to rationalize the details systematically. Unicode 3.1 was the first version to formally introduce Noncharacter_Code_Point as a property and apply it to FFFE/FFFF (as well as the other noncharacters). Unicode 2.0 introduced the concept of Unicode scalar value and established the framework of definitions and conformance clauses now familiar in Chapter 3 (although it was pretty rough around the edges back then). It also documented UTF-8 (although at that point it was in an annex still), and that *required* a mapping between the UTF-16 and UTF-8 form of 0xnFFFE and 0xnFFFF on each plane. The Age value derives from that. U+FFFE and U+FFFF themselves were given Age=1.1 because they were part of Unicode 1.1 before Unicode 2.0 formally documented the addition of the rest of the planes. Earlier still, when Unicode was still trying to be a pure 16-bit encoding, FFFE and FFFF were simply outside the codespace. Incidentally, the property Age wasn't introduced until Unicode 3.2, to technically speaking it didn't exist before then, either. However, assignments of Age values were derived retroactively backwards to Version 1.1 for parceling out the initial assignments as of Unicode 3.2. Note also that although the majority of the repertoire in Unicode 1.1 actually was already assigned as of Unicode 1.0, no attempt was made to assign Age=1.0 to any characters, because of the churn and renaming that occurred as a result of the Unicode 1.0 and ISO 10646-1 merger effort back in the early 1990's. --Ken _______________________________________________ Unicode mailing list [email protected] http://unicode.org/mailman/listinfo/unicode
