BabelStone Blog

Saturday, 23 December 2006

Phags-pa Shaping Behaviour

Now that I have released my first Phags-pa font, I thought it would be useful to discuss Phags-pa shaping behaviour, as very few people are familiar with the script, and it is quite complex. Further information on the Phags-pa script, its encoding model and shaping behaviour can be found in Section 10.3 of The Unicode Standard version 5.0.

First of all, here is a table of the encoded Phags-pa characters (note that you need to have BabelStone Phags-pa Book installed to see the Phags-pa characters; also note that with IE the characters should be oriented vertically, but with other browsers they may not be).

Table of Encoded Phags-pa Characters

Code Point	Character	Character Name	Usage
U+A840	ꡀ	PHAGS-PA LETTER KA	Chinese Mongolian Sanskrit Tibetan
U+A841	ꡁ	PHAGS-PA LETTER KHA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A842	ꡂ	PHAGS-PA LETTER GA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A843	ꡃ	PHAGS-PA LETTER NGA	Chinese Mongolian Sanskrit Tibetan
U+A844	ꡄ	PHAGS-PA LETTER CA	Chinese Tibetan
U+A845	ꡅ	PHAGS-PA LETTER CHA	Chinese Mongolian Tibetan Uighur
U+A846	ꡆ	PHAGS-PA LETTER JA	Chinese Mongolian Tibetan Uighur
U+A847	ꡇ	PHAGS-PA LETTER NYA	Chinese Sanskrit Tibetan
U+A848	ꡈ	PHAGS-PA LETTER TA	Chinese Mongolian Sanskrit Tibetan
U+A849	ꡉ	PHAGS-PA LETTER THA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A84A	ꡊ	PHAGS-PA LETTER DA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A84B	ꡋ	PHAGS-PA LETTER NA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A84C	ꡌ	PHAGS-PA LETTER PA	Chinese Mongolian Sanskrit Tibetan
U+A84D	ꡍ	PHAGS-PA LETTER PHA	Chinese Sanskrit Tibetan
U+A84E	ꡎ	PHAGS-PA LETTER BA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A84F	ꡏ	PHAGS-PA LETTER MA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A850	ꡐ	PHAGS-PA LETTER TSA	Chinese Sanskrit Tibetan
U+A851	ꡑ	PHAGS-PA LETTER TSHA	Chinese Mongolian Sanskrit Tibetan
U+A852	ꡒ	PHAGS-PA LETTER DZA	Chinese Sanskrit Tibetan
U+A853	ꡓ	PHAGS-PA LETTER WA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A854	ꡔ	PHAGS-PA LETTER ZHA	Chinese Tibetan
U+A855	ꡕ	PHAGS-PA LETTER ZA	Chinese Mongolian Tibetan
U+A856	ꡖ	PHAGS-PA LETTER SMALL A	Chinese Mongolian Sanskrit Tibetan Uighur
U+A857	ꡗ	PHAGS-PA LETTER YA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A858	ꡘ	PHAGS-PA LETTER RA	Mongolian Sanskrit Tibetan Uighur
U+A859	ꡙ	PHAGS-PA LETTER LA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A85A	ꡚ	PHAGS-PA LETTER SHA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A85B	ꡛ	PHAGS-PA LETTER SA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A85C	ꡜ	PHAGS-PA LETTER HA	Chinese Mongolian Sanskrit Tibetan Uighur
U+A85D	ꡝ	PHAGS-PA LETTER A	Chinese Mongolian Sanskrit Tibetan Uighur
U+A85E	ꡞ	PHAGS-PA LETTER I	Chinese Mongolian Sanskrit Tibetan Uighur
U+A85F	ꡟ	PHAGS-PA LETTER U	Chinese Mongolian Sanskrit Tibetan Uighur
U+A860	ꡠ	PHAGS-PA LETTER E	Chinese Mongolian Sanskrit Tibetan Uighur
U+A861	ꡡ	PHAGS-PA LETTER O	Chinese Mongolian Sanskrit Tibetan Uighur
U+A862	ꡢ	PHAGS-PA LETTER QA	Mongolian Uighur
U+A863	ꡣ	PHAGS-PA LETTER XA	Chinese Mongolian
U+A864	ꡤ	PHAGS-PA LETTER FA	Chinese Uighur
U+A865	ꡥ	PHAGS-PA LETTER GGA	Unknown
U+A866	ꡦ	PHAGS-PA LETTER EE	Chinese Mongolian Uighur
U+A867	ꡧ	PHAGS-PA SUBJOINED LETTER WA	Chinese Sanskrit Tibetan
U+A868	ꡨ	PHAGS-PA SUBJOINED LETTER YA	Chinese Sanskrit Tibetan
U+A869	ꡩ	PHAGS-PA LETTER TTA	Sanskrit
U+A86A	ꡪ	PHAGS-PA LETTER TTHA	Sanskrit
U+A86B	ꡫ	PHAGS-PA LETTER DDA	Sanskrit
U+A86C	ꡬ	PHAGS-PA LETTER NNA	Sanskrit
U+A86D	ꡭ	PHAGS-PA LETTER ALTERNATE YA	Chinese
U+A86E	ꡮ	PHAGS-PA LETTER VOICELESS SHA	Chinese
U+A86F	ꡯ	PHAGS-PA LETTER VOICED HA	Chinese
U+A870	ꡰ	PHAGS-PA LETTER ASPIRATED FA	Chinese
U+A871	ꡱ	PHAGS-PA SUBJOINED LETTER RA	Sanskrit Tibetan
U+A872	ꡲ	PHAGS-PA SUPERFIXED LETTER RA	Tibetan
U+A873	ꡳ	PHAGS-PA LETTER CANDRABINDU	Sanskrit
U+A874	꡴	PHAGS-PA SINGLE HEAD MARK	Tibetan
U+A875	꡵	PHAGS-PA DOUBLE HEAD MARK	Tibetan
U+A876	꡶	PHAGS-PA MARK SHAD	Tibetan
U+A877	꡷	PHAGS-PA MARK DOUBLE SHAD	Tibetan

1. Ligation

Phags-pa characters form syllable units in which the letters comprising a syllable ligate together, and each syllable unit is separated from each other by white space. Letters normally ligate along a stem running down the right side, but mirrored letters used for Sanskrit ligate along the left side, and the vowel o joins down a central stem. Examples of words in different languages are given below.

Chinese

mung gu wun ꡏꡟꡃ ꡂꡟ ꡓꡟꡋ

mengguwen 蒙古文 "Mongolian"

Mongolian

ta layi ꡈ ꡙꡗꡞ

dalai ᠳᠠᠯᠠᠢ "ocean"

Note that layi is considered a single syllable as ayi is used to represent a final /ai/ diphthong in Mongolian and Sanskrit.

Sanskrit

pra tish tthi te ꡌꡱ ꡈꡞꡚ ꡪꡞ ꡈꡠ

pratiṣṭhite

Tibetan

sangs rgyas ꡛꡃꡛ ꡲꡂꡨꡛ

sangs-rgyas "Buddha"

Uighur

quth luq ꡢꡟꡉ ꡙꡟꡢ

qutlugh "good fortune"

2. Vowel Forms

The four vowels I, U, E and O have distinct positional forms, as shown in the table below.

3. Mirrored Letters

A mirrored series of the letters TA, THA, DA and NA are used in the Sanskrit Phags-pa inscriptions at Juyongguan 居庸關. These letters, which represent the Sanskrit retroflex letters ṭa, ṭha, ḍa and ṇa, are not found in any other extant Phags-pa text or inscription. For example, on the 1348 Dunhuang inscription Sanskrit maṇi is represented in Phags-pa script as MA NI ꡏ ꡋꡞ with no mirroring. Note that a mirrored letter SHA representing Sanskrit ṣha does not occur, and so the kṣh combination is written with the Phags-pa letters KA followed by unmirrored SHA in the Juyongguan inscriptions.

These four mirrored letters affect the shape of the following letter as follows :

After the letters TTA, TTHA, DDA or NNA (or the mirrored form of the letters Subjoined YA and HA) a following letter I, U or E is mirrored, although in some places in the Juyongguan inscriptions the letter I is not mirrored after the letter TTHA.
After the letter NNA a following letter Subjoined YA is mirrored.
After the letter DDA a following letter HA is mirrored.
After the letters TTA or TTHA a following letter Small A may be mirrored, but in most instances in the Juyongguan inscriptions the Small A is not mirrored, presumably because a mirrored Small A is identical to the letter SHA.

When mirrored letters are joined together they ligate along a lefthand stem rather than the righhand stem as is normally the case. If the letter TTHA is followed by an unmirrored Small A the ligature may be on the right or the left side.

As the mirrored forms of the letters I, U, E, Small A, HA and Subjoined YA are contextual glyph variants they are not encoded as separate characters, but are automatically selected by the rendering system as appropriate. In practical terms this means that an OpenType Phags-pa font will have normal and mirrored forms of theses characters and apply a substitution rule to replace the normal form with the mirrored form after a mirrored form glyph. These rules are applied automatically by the rendering system so that the normal or mirrored form, as appropriate for the particular context, is displayed automatically without any need for user intervention.

My Phags-pa fonts follow the agreed shaping behaviour for Phags-pa (see section 10.3 of The Unicode Standard version 5.0), which is to mirror the glyph for the letters Small A [U+A856], HA [U+A85C], I [U+A85E], U [U+A85F], E [U+A860] and Subjoined YA [U+A868] after the letters TTA [U+A869], TTHA [U+A86A], DDA [U+A86B] or NNA [U+A86C] or after another mirrored glyph.

However, there are times when the user may wish to override the default mirroring behaviour, for example in order to display mirrored glyph forms in isolation or in order to represent those examples of unmirrored I after the letter TTHA or unmirrored Small A after the letters TTA and TTHA that occur in the Juyongguan inscriptions. This is acheived by means of variation selectors. For Phags-pa VS1 [U+FE00] is used to produce the opposite form of a reversing letter that would be expected from its context. This is an important distinction to note, as it differs from the behaviour of mathematical standardized variants, where a particular variation sequence always produces the same glyph. Thus for Phags-pa the sequence U, VS1 <U+A85F U+FE00> will produce an unmirrored letter U glyph if it occurs after one of the letters TTA, TTHA, DDA or NNA or after a mirrored glyphform of the letters I, U, E, Small A, HA or Subjoined YA, but will produce a mirrored letter U if the sequence occurs after any other Phags-pa letter or in isolation.