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Diffstat (limited to 'elsie.nci.nih.gov/src/Theory')
| -rw-r--r-- | elsie.nci.nih.gov/src/Theory | 23 |
1 files changed, 10 insertions, 13 deletions
diff --git a/elsie.nci.nih.gov/src/Theory b/elsie.nci.nih.gov/src/Theory index 4f9c226..6bed91f 100644 --- a/elsie.nci.nih.gov/src/Theory +++ b/elsie.nci.nih.gov/src/Theory @@ -173,7 +173,7 @@ like 'EST' to be compatible with human tradition and POSIX. Here are the general rules used for choosing time zone abbreviations, in decreasing order of importance: - Use abbreviations that consist of three or more ASCII letters. + Use three or more characters that are ASCII alphanumerics or '+' or '-'. Previous editions of this database also used characters like ' ' and '?', but these characters have a special meaning to the shell and cause commands like @@ -181,19 +181,16 @@ in decreasing order of importance: to have unexpected effects. Previous editions of this rule required upper-case letters, but the Congressman who introduced Chamorro Standard Time - preferred "ChST", so the rule has been relaxed. - - This rule guarantees that all abbreviations could have - been specified by a POSIX TZ string. POSIX - requires at least three characters for an - abbreviation. POSIX through 2000 says that an abbreviation - cannot start with ':', and cannot contain ',', '-', - '+', NUL, or a digit. POSIX from 2001 on changes this - rule to say that an abbreviation can contain only '-', '+', + preferred "ChST", so lower-case letters are now allowed. + Also, POSIX from 2001 on relaxed the rule to allow '-', '+', and alphanumeric characters from the portable character set - in the current locale. To be portable to both sets of - rules, an abbreviation must therefore use only ASCII - letters. + in the current locale. In practice ASCII alphanumerics and + '+' and '-' are safe in all locales. + + In other words, in the C locale the POSIX extended regular + expression [-+[:alnum:]]{3,} should match the abbreviation. + This guarantees that all abbreviations could have been + specified by a POSIX TZ string. Use abbreviations that are in common use among English-speakers, e.g. 'EST' for Eastern Standard Time in North America. |