21.4.4 HTML Cross-reference 8-bit Character Expansion

Usually, characters other than plain 7-bit ASCII are transformed into the corresponding Unicode code point(s) in Normalization Form C, which uses precomposed characters where available. (This is the normalization form recommended by the W3C and other bodies.) This holds when that code point is 0xffff or less, as it almost always is.

These will then be further transformed by the rules above into the string ‘_hhhh’, where hhhh is the code point in hex.

For example, combining this rule and the previous section:

@node @b{A} @TeX{} @u{B} @point{}@enddots{}
⇒ A-TeX-B_0306-_2605_002e_002e_002e

Notice: 1) @enddots expands to three periods which in turn expands to three ‘_002e’’s; 2) @u{B} is a ‘B’ with a breve accent, which does not exist as a pre-accented Unicode character, therefore expands to ‘B_0306’ (B with combining breve).

When the Unicode code point is above 0xffff, the transformation is ‘__xxxxxx’, that is, two leading underscores followed by six hex digits. Since Unicode has declared that their highest code point is 0x10ffff, this is sufficient. (We felt it was better to define this extra escape than to always use six hex digits, since the first two would nearly always be zeros.)

This method works fine if the node name consists mostly of ASCII characters and contains only few 8-bit ones. But if the document is written in a language whose script is not based on the Latin alphabet (for example, Ukrainian), it will create file names consisting almost entirely of ‘_xxxx’ notations, which is inconvenient and all but unreadable. To handle such cases, makeinfo offers the --transliterate-file-names command line option. This option enables transliteration of node names into ASCII characters for the purposes of file name creation and referencing. The transliteration is based on phonetic principles, which makes the generated file names more easily understandable.

For the definition of Unicode Normalization Form C, see Unicode report UAX#15, http://www.unicode.org/reports/tr15/. Many related documents and implementations are available elsewhere on the web.