r.ermers@hccnet.nl said this at Tue, 21 Dec 2004 08:56:40 +0100:
In Latex the combination \"{a} can mean two things: 1. in most fonts: show the charachter on the a given numerical position, which means that there is one character ä.
2. in some other fonts \"{a} means: combine " with a and make an ä. This means that " is combined with the character on the numerical position of a. TeX does this very well and thus construes very acceptable diacritical signs like \"{q}, \d{o}, \v{o}, which do not exist in regular fonts.
Robert, That's a helpful explanation. I'll try to expand on that in the ConTeXt case, just in case people are curious or are led into thinking it's just the same: In ConTeXt, the combination \"{a} means one thing: \adiaeresis (see enco- acc). This \adiaeresis can mean one of two things, depending on the encoding: 1. Numerical position, or 2. The fallback case (defined in enco-def), where a diaeresis/umlaut is placed atop an 'a' glyph. Hyphenation implications as Hans described. The interesting/helpful thing about ConTeXt is that internally, that glyph is given a consistent name, no matter how it is input or output. So, if you type ä in your given input regime, and that encoding is properly set, that numerical ä (e.g., character #228 in the windows regime) is mapped to \adiaeresis. Wanna know what happens in UTF-8? Here's my 'simplified' explanation: In a UTF-8 bytestream, that character "ä" is signified by two bytes: 0xC3, 0xA4. That first byte triggers a conversion of both bytes into two different bytes, the actual Unicode number, 0x00 0xE4 (or: 0, 228). ConTeXt then looks into internal hashes set up (in this case, the unic- 000 vector), looks at the 228th element, and sees that it's \adiaeresis. Things then proceed as normal. :) (It's also interesting to note that for PostScript and TrueType fonts, that number > name > number (glyph) mapping happens yet again in the driver. But all that is outside of TeX proper, so to say any more would be confusing.) -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Adam T. Lindsay, Computing Dept. atl@comp.lancs.ac.uk Lancaster University, InfoLab21 +44(0)1524/510.514 Lancaster, LA1 4WA, UK Fax:+44(0)1524/510.492 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-