/ 
Text-BibTeX-1.00
/ bt_misc

NAME

bt_misc - miscellaneous BibTeX-like string-processing utilities

SYNOPSIS

char * bt_purify_string (const char *string, btshort options);
char * bt_change_case (bt_errors *errs, char transform,
                       const char *string, btshort options);

DESCRIPTION

Both functions return a newly allocated string (free it with free()); the input is not modified. Text may be UTF-8: characters are classified and case-mapped according to Unicode, never byte by byte, and bytes that are not valid UTF-8 are treated as characters with no properties (so other encodings pass through unharmed). TeX control sequences, which are always ASCII letters, are handled as described below.

bt_purify_string()
char * bt_purify_string (const char *string, btshort options);

"Purifies" a string in the BibTeX way (usually used for generating sort keys). options is currently unused; just set it to zero for future compatibility. Purification consists of copying alphanumeric characters (letters and digits in any script, along with any combining marks attached to them), converting hyphens and ties to space, copying spaces, and skipping (almost) everything else.

"Almost" because "special characters" (used for accented and non-English letters) are handled specially. Recall that a BibTeX special character is any brace-group that starts at brace-depth zero whose first character is a backslash. For instance, the string

{\foo bar}Herr M\"uller went from {P{\r r}erov} to {\AA}rhus

contains two special characters: "{\foo bar}" and "\AA". Neither the \"u nor the \r r are special characters, because they are not at the right brace depth.

Special characters are handled as follows: if the control sequence (the TeX command that follows the backslash) is recognized as one of LaTeX's "foreign letters" (\oe, \ae, \o, \l, \ae, \ss, plus uppercase versions), then it is converted to a reasonable English approximation by stripping the backslash and converting the second character (if any) to lowercase; thus, {\AA} in the above example would become simply Aa. All other control sequences in a special character are stripped, as are all non-alphabetic characters.

For example the above string, after "purification," becomes

barHerr Muller went from Pr rerov to Aarhus

Obviously, something has gone wrong with the word P{\r r}erov (a town in the Czech Republic). The accented `r' should be a special character, starting at brace-depth zero. If the original string were instead

{\foo bar}Herr M\"uller went from P{\r r}erov to {\AA}rhus

then the purified result would be more sensible:

barHerr Muller went from Prerov to Aarhus

Note the use of a "nonsense" special character {\foo bar}: this trick is often used to put certain text in a string solely for generating sort keys; the text is then ignored when the document is processed by TeX (as long as \foo is defined as a no-op TeX macro). This assumes, of course, that the output is eventually processed by TeX; if not, then this trick will backfire on you.

Also, bt_purify_string() is adequate for generating sort keys when you want to sort according to English-language conventions. To follow the conventions of other languages, use a collation library (such as Unicode::Collate) on the purified string.

bt_change_case()
char * bt_change_case (bt_errors *errs, char transform,
                       const char *string, btshort options);

Converts a string to lowercase, uppercase, or "non-book title capitalization", with special attention paid to BibTeX special characters and other brace-groups. The form of conversion is selected by the single character transform: 'u' to convert to uppercase, 'l' for lowercase, and 't' for "title capitalization"; any other value is a usage error (reported in errs, and NULL is returned). options is currently unused; set it to zero for future compatibility.

Case conversion uses the full Unicode case mappings, so the result may be longer than the input (eg. "ß" uppercases to "SS"). For title capitalization the first character of a sentence is converted to titlecase (which only differs from uppercase for a few digraphs such as "dž").

Lowercase and uppercase conversion are obvious, with the proviso that text in braces is treated differently (explained below). Title capitalization simply means that everything is converted to lowercase, except the first letter of the first word, and words immediately following a colon or sentence-ending punctuation. For instance,

Flying Squirrels: Their Peculiar Habits. Part One

would be converted to

Flying squirrels: Their peculiar habits. Part one

Text within braces is handled as follows. First, in a "special character" (see above for definition), control sequences that constitute one of LaTeX's non-English letters are converted appropriately---e.g., when converting to lowercase, \AE becomes \ae). Any other control sequence in a special character (including accents) is preserved, and all text in a special character, regardless of depth and punctuation, is converted to lowercase or uppercase. (For "title capitalization," all text in a special character is converted to lowercase.)

Brace groups that are not special characters are left completely untouched: neither text nor control sequences within non-special character braces are touched.

For example, the string

A Guide to \LaTeXe: Document Preparation ...

would, when transform is 't' (title capitalization), be converted to

A guide to \latexe: Document preparation ...

which is probably not the desired result. A better attempt is

A Guide to {\LaTeXe}: Document Preparation ...

which becomes

A guide to {\LaTeXe}: Document preparation ...

However, if you go back and re-read the description of bt_purify_string(), you'll discover that {\LaTeXe} here is a special character, but not a non-English letter: thus, the control sequence is stripped. Thus, a sort key generated from this title would be

A Guide to  Document Preparation

...oops! The right solution (and this applies to any title with a TeX command that becomes actual text) is to bury the control sequence at brace-depth two:

A Guide to {{\LaTeXe}}: Document Preparation ...

SEE ALSO

btparse

AUTHOR

Greg Ward <gward@python.net>