This page brings together basic information about the Tai Tham (Lanna) script and its use for the Northern Thai language. It aims to provide a brief, descriptive summary of the modern, printed orthography and typographic features, and to advise how to write Northern Thai using Unicode.
Good Tai Tham fonts are hard to find, especially for Northern Thai. The default font used for Northern Thai in this page is Hariphunchai. Discussions are under way at the Unicode Consortium that may change the ordering of character sequences in the future, so the order of characters in this page reflects what the font expects in order to display correctly.
Sample
Select part of this sample text to show a list of characters, with links to more details.
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Northern Thai is is spoken by the people of Lanna, Thailand, with a smaller community of Lanna speakers in northwestern Laos. Few of the six million speakers of Northern Thai are literate in the Tai Tham script, although there is some rising interest in the script among the young. Since the beginning of the 20th century, the Thai script has been used for the Northern Thai language, although the fact that Thai only has 5 tones to Northern Thai's 6 makes this problematic.
Use of the Lanna traditional script is now largely limited to Buddhist temples, where many old sermon manuscripts are still in active use. There is no active production of literature in the traditional alphabet. The modern pronunciation differs from that prescribed in spelling rules.
ᨲ᩠ᩅᩫᨾᩮᩥᩬᨦᨣᩤᩴᨾᩮᩨᩬᨦ
In the Thai script this is คำเมือง.
The Lana script is derived from Mon, and before that Pallava.
The Tai Tham script is an abugida, ie. consonants carry an inherent vowel sound that is overridden using vowel signs. In Tai Tham, consonants carry an inherent vowel. See the table to the right for a brief overview of features for the modern Northern Thai orthography.
Northern Thai text runs left to right in horizontal lines.
Words are not separated by spaces, however syllables may be separated by ZWSP, as long as they don't fall inside a stack.
Each onset consonant is associated with a high, mid, or low class related to tone. Tone is indicated by a combination of the consonant class, the syllable type (checked/unchecked), plus any tone mark. ❯ consonants
Tai Tham has stacked consonants, but these do not necessarily indicate consonant clusters. The script is unusual in that any consonant in a stack can retain its inherent vowel, or be associated with a vowel sign. The sakot, which produces stacks, is never visible. ❯ clusters
Stacks can span word boundaries.
Syllable-initial clusters use 2 dedicated code points for the medial l, and a subjoined letter for medial w. ❯ onsets
Syllable-final consonant sounds can be written using 6 special diacritics, but otherwise use ordinary letters, which may or may not be subjoined depending on the context. ❯ finals
The Northern Thai orthography has an inherent vowela, and represents vowels using 18 vowel signs (including 5 pre-base vowels), and 3 consonants. However, unlike Thai and Lao, all vowel signs are combining marks, and are stored after the base character. Vowels are often written differently when they appear in a closed vs. open syllable. ❯ vowels
This page lists 29 composite vowels (made from 9 vowel signs, and 3 consonants/diacritics). Composite vowels can involve up to 5 glyphs, which can surround the base consonant(s) on up to 4 sides, eg. ❯ composite_vowels
ᨠᩮᩨᩬᩋᩡ
Northern Thai and Khün not only use a slightly different set of characters, but a number of characters have consistently divergeant shapes.
Click on the sounds to reveal locations in this document where they are mentioned.
Phones in a lighter colour are non-native or allophones.
Vowel sounds
Plain vowels
Diphthongs
Consonant sounds
labial
dental
alveolar
post-
alveolar
palatal
velar
glottal
stops
pb
td
k
ʔ
aspirated
pʰ
tʰ
affricates
t͡ɕ
fricatives
f
s
x
h
nasals
m
n
ɲ
ŋ
approximants
w
l
j
The glottal stop is pronounced after short open vowels. An initial glottal stop is also pronounced before independent vowels (see standalone).
Syllable-final
labial
dental
alveolar
post-
alveolar
palatal
velar
glottal
stop
p̚
t̚
k̚
ʔ
nasal
m
n
ŋ
approximant
w
j
All final stops are unreleased@Wikipedia,https://en.wikipedia.org/wiki/Northern_Thai_language#Final_consonants.
Tone
The Chiang Mai dialect of Northern Thai has 6 tones. They are illustrated in fig_tones, which is taken from Wikipedia.
The six tones of Northern Thai.
Wikipedia provides the following information for the 6 phonemic tones for unchecked syllables in the Changmai dialect of Northern Thai. (It also has sound recordings.)wnl,#Consonants
Tone
Representations
Example
low-rising
˨˦
24
ǎ
ᩉᩖᩮᩢᩣ
mid-low
˨
22
à
ᩉᩖᩮᩢᩣ᩵
high-falling
glottalised
˥˧
53
a᷇
ᩉᩖᩮᩢᩣ᩶
mid-high
˧
33
ā
ᩃᩮᩢᩣ
falling
˥˩
51
â
ᩃᩮᩢᩣ᩵
high rising-falling
glottalised
˦˥˦
545
á
ᩃᩮᩢᩣ᩶
This is the list for checked syllables.wnl,#Consonants
Tone
Representations
Example
low-rising
˨˦
24
ǎ
ᩉᩖᩢᨠ
high-falling
˥
55
a᷇
ᩃᩢ᩠ᨠ
low
˨
22
à
ᩉᩖᩣ᩠ᨠ
falling
˥˩
51
â
ᩃᩣ᩠ᨠ
The mapping of tones to characters is described in tones.
Vowels
Dashes are used to indicate the location of a consonant or consonant cluster. Prescript vowel signs have been stored before the hyphen because of the limitations of the font, but in reality all vowel signs should occur after the consonant they modify.
The Northern Thai orthography has an inherent vowela, and represents vowels using 19 dependent vowel marks (including 5 pre-base vowel signs), and 3 consonants (2 of which as subjoined forms). Unlike Thai and Lao, all vowel signs are combining marks, and are stored after the base character. Vowels are often written differently when they appear in a closed vs. open syllable.
This page lists 29 composite vowels (made from 9 vowel signs, and 3 consonants/diacritics). Composite vowels can involve up to 5 glyphs, which can surround the base consonant(s) on up to 4 sides, eg.
ᨠᩮᩨᩬᩋᩡ
For a mapping of sounds to graphemes see vowel_mappings.
Inherent vowel
a following a consonant is not written, but is seen as an inherent part of the consonant letter, so ka is written by simply using the consonant letter.
ᨠ
ka[U+1A20 LETTER HIGH KA]
Vowel signs
Non-inherent vowel sounds that follow a consonant can be represented using vowel signs, eg.
ᨠᩥ
ki[U+1A20 LETTER HIGH KA + U+1A65 VOWEL SIGN I]
The majority of code points used to represent vowel sounds are combining marks. However, Northern Thai also uses some consonants. Many vowel sounds are represented by a combination of code points (see composite_vowels), such as the following example, where the consonant base is followed by 4 vowel signs, which are displayed around the base.
ᨠᩮᩥᩬᩡ
kɤʔ[U+1A20 LETTER HIGH KA + U+1A6E VOWEL SIGN E + U+1A65 VOWEL SIGN I + U+1A6C VOWEL SIGN OA BELOW + U+1A61 VOWEL SIGN A]
In principle, all vowel signs are typed and stored after the base consonant, whether or not they precede it when displayed. The font takes care of the glyph positioning. However, the Unicode Consortium is currently examining the encoding model for Tai Tham. There is a possibility that pre-base vowel signs may be stored before the consonant in future.
Eight vowel signs are spacing marks, meaning that they consume horizontal space when added to a base consonant.
Combining marks used for vowels
Northern Thai uses the following dedicated combining marks for vowels. They may be used on their own, or in combination with others (see composite_vowels).
ᩴ [U+1A74 TAI THAM SIGN MAI KANG] is used with many words to represent a syllable-final -m or -ŋ (see finals), but it also functions as a vowel when it appears alone or as a component of a composite vowel.
ᨣᩴ
The sound it represents may be ambiguous. For instance, compare the example just above with the one below, where it fulfills the role of syllable-final consonant.
ᨶᩣᩴ
Pre-base vowel signs
ᩮ␣ᩰ␣ᩯ␣ ␣ᩱ␣ᩲ
Five vowel signs appear to the left of the base consonant letter or cluster.
A prebase vowel sign appears to the left of the consonant after which it is pronounced.details
ᨯᩱ᩶
These combining marks are stored after the base consonant: the rendering process places the glyph before that of the base consonant. However, the Unicode Consortium is currently examining the coding model for Tai Tham. There is a possibility that pre-base vowel signs may be stored before the consonant in future. Also, some fonts already require this kind of handling, especially for dealing with complex combinations of characters.
Consonants pronounced as vowels
The following are also involved in the production of vowel sounds.
᩠ᨿ␣᩠ᩅ␣ᩋ
The sequence
᩠ᩅ [U+1A60 TAI THAM SIGN SAKOT + U+1A45 TAI THAM LETTER WA]
often represents a medial w – especially common after x or k but also occurring after a (dwindling) number of other consonants. However, when no other vowel signs follow (ie. when the inherent vowel is involved), it represents the diphthong ua rather than -wa.
Both of these characters also appear as a component in some of the composite vowels described below.
ᩋ [U+1A4B TAI THAM LETTER A] on its own represents the standalone version of the inherent vowel ʔa, and is used as a base for vowel signs when writing other standalone vowels (see standalone). However, it also makes an appearance as a vowel component in 2 composite vowels.
Composite vowels
This section lists vowel sounds represented by combinations of the above characters (this list is possibly incomplete).
Some represent plain vowel sounds:
ᩮᩢ␣ᩮᩡ␣ᩰᩡ␣ᩰᩫ␣ᩯᩢ␣ᩯᩡ␣ᩮᩥᩢ␣ᩮᩥᩬᩡ␣ᩮᩥ␣ᩮᩥᩬ␣ᩢᩬ␣ᩰᩬᩡ␣ᩬᩴ
The other composites represent diphthongs, which generally end in one of -a, -j or -w.
᩠ᨿᩮ␣᩠ᨿᩮᩡ␣ᩢ᩠ᨿ␣ᩮᩥᩢᩬ␣ᩮᩨᩢᩬ␣ᩮᩨᩬ␣ᩮᩨᩬᩋ␣ᩮᩨᩬᩋᩡ␣᩠ᩅᩫ␣᩠ᩅᩫᩡ␣᩠ᩅᩢ␣᩠ᩅ᩠ᨿ␣ᩱ᩠ᨿ␣ᩣ᩠ᨿ␣ᩮᩢᩣ␣ᩮᩢᩤShow which combinations contain a given character:
The following list shows where vowel signs are positioned around a base consonant to produce vowels, and how many instances of that pattern there are. The figure after the + sign represents combinations of Unicode characters, The list includes subjoined WA and YAand the postfixed ᩋ.
Locations where vowel elements can appear, including in complex vowels.
Vowel components can occur concurrently on 4 sides of the base, eg. ᩮᩬᩥᩡ.
Characters that don't appear in the combinations:
ᩦ␣ᩧ␣ᩩ␣ᩪ␣ᩲ␣ᩳ
Standalone vowels
Vowel signs
For vowels not preceded by a consonant Northern Thai generally uses ᩋ [U+1A4B TAI THAM LETTER A] with one or more vowel signs, eg. ᩋᩧ᩠ᨷ
Independent vowels
Some standalone vowels can be represented using a set of independent vowel letters. The set includes a consonant character which used alone represents the inherent vowel sound, but the list only covers a small number of possible vowel sounds.
ᩍ␣ᩎ␣ᩏ␣ᩐ␣ᩑ␣ᩋ
The 5 independent vowel letters are used in syllable-initial position for certain words, but for other words the base+vowel sign approach may be used.
ᩑᨠ
ᩋᩮ᩠ᨶ
Vowel sounds mapped to characters
This section maps Northern Thai vowel sounds to common graphemes in the Lanna orthography, where open indicates an open syllable, closed a closed syllable, and standalone a standalone vowel. Click on a grapheme to find other mentions on this page (links appear at the bottom of the page). Click on the character name to see examples and for detailed descriptions of the character(s) shown.
Sounds listed as 'infrequent' are allophones, or sounds used for foreign words, etc.
For some diphthongs ending in -j or -w, Owen indicates that phonetic sequences exist. but offers no examples. Based on other examples, it is assumed here that -j is formed using sakot+ya, and -w using sakot+wa, except where the preceding vowel sign extends below the baseline (such as for uj).
With the high/low categorisation of consonants, Northern Thai writing generally needs only the two combining tone marks below to indicate one of the possible phonetic tones.
᩵␣᩶
If there is a vowel over or below a consonant or consonant stack, the tone mark follows the vowel in storage, and is displayed above or alongside the vowel.
Otherwise, the tone is input after the consonant, ie. before a vowel sign that is displayed to the right or below, and appears over the consonant. e
The default fonts used here expect the tone to be typed after a lefted vowel if there is one; after a vowel above, if there is one; before a vowel to the right; and doesn't seem to matter wrt low vowel. See this test. Noto agrees except for lefted vowels.
The following chart shows how to tell which tones are associated with a syllable.
Consonant
Checked?
Tone mark
Tone
high
checked
short
2
long
3
open
-
1
᩵
3
᩶
5
mid
checked
short
2
long
3
open
-
2
᩵
3
᩶
5
᩷
2
᩸
1
᩹
6
low
checked
short
6
long
4
open
-
2
᩵
4
᩶
6
Consonants
Each onset consonant is associated with a high, mid, or low class related to tone. Tone is indicated by a combination of the consonant class, the syllable type (checked/unchecked), plus any tone mark.
Tai Tham has stacked consonants, but these do not necessarily indicate consonant clusters. The script is unusual in that any consonant in a stack can retain its inherent vowel, or be associated with a vowel sign. The sakot, which produces stacks, is never visible.
Stacks can span word boundaries.
Syllable-initial clusters use 2 dedicated code points for the medial l, and a subjoined letter for medial w.
Syllable-final consonant sounds can be written using 6 special diacritics, but otherwise use ordinary letters, which may or may not be subjoined depending on the context.
The lists below show consonants in the Northern Thai repertoire. The letters h, m, and l indicate the class of the consonant. This list includes some sequences to indicate high class forms when there is no single letter for that. Where 2 pronunciations are given, the first is for syllable-initial, and the second for syllable-final use.
ʨʰ is not a native Northern Thai sound, but rather associated with reading the alphabet out loud and in learned pronunciation of Pali loanwords.o,142
A few consonants have different phonetic realisations in Tai Khün, and ᨢ [U+1A22 TAI THAM LETTER HIGH KXA] is not used by Tai Khün.
High class nasals & liquids with HA
High and low consonants usually come in pairs, but where they don't the high variant is normally given by subjoining the low consonant below ᩉ [U+1A49 TAI THAM LETTER HIGH HA].
ᩉ᩠ᨶᩧ᩵ᨦ
These combinations are included in the charts above.
It can be used with vowels at the beginning of a syllable, or on its own to indicate a standalone sound corresponding to the inherent vowel (see standalone).
ᩋᩧ᩠ᨷ
ᩋᩉ᩠ᨿᩢᨦ
It has very different shapes in Northern Thai text ᩋ and Khün text ᩋ.
Special consonants
ᩛ␣ᩓ␣ᩔ
The first of these is a special-use consonant diacritic. The second two are ligatures.
Tai Tham is unusual in that subjoined consonants do not only appear where there are consonant clusters. There is a natural tendency to attempt to stack consonants, usually 2 high, whenever possible.
᩠U+1A60 TAI THAM SIGN SAKOT is the (always) invisible character used to produce the subjoined form of a consonant, eg. compare the following:
ᨠᨠ
kk[U+1A20 TAI THAM LETTER HIGH KA + U+1A20 TAI THAM LETTER HIGH KA]
ᨠ᩠ᨠ
kk[U+1A20 TAI THAM LETTER HIGH KA + U+1A60 TAI THAM SIGN SAKOT + U+1A20 TAI THAM LETTER HIGH KA]
Sakot doesn't always kill the inherent vowel between two consonants, nor does it create conjuncts, in the sense of merged shapes, but subjoined forms of consonants typically have a different and smaller shape compared to the standard form.
Sakot can follow a vowel sign. For example, in the following word the sakot is used to position the final consonant in the syllable below the vowel sign. This is quite common.
ᩈᩣ᩠ᨾ
A subjoined consonant can also follow a digit.
᪓᩠ᨴ
Subjoined consonants are not only syllable-final consonants. The first consonant in a following syllable may also be subjoined, eg. (final r is pronounced as n).eu,654
ᨳ᩠ᨶᩫ᩻ᩁ
This list shows consonants in their normal and subjoined forms. Not all consonants traditionally have subjoined forms, but modern innovations in borrowed terminology suggest that fonts should provide them for all consonants except the old vocalic letters.u,654 You may find that the font applied here doesn't handle all combinations well.
᩻ [U+1A7B TAI THAM SIGN MAI SAM]
is used in Northern Thai to identify double-acting consonants, or to indicate that a subjoined consonant begins a new syllable, eg. compare the following (where final r is pronounced as n).e
A medial -w also occurs, but there is no dedicated character for it. Instead it is produced using an ordinary WA which is subjoined using the sakot, ie. ᩠ᩅ [U+1A60 TAI THAM SIGN SAKOT + U+1A45 TAI THAM LETTER WA]. Such clusters are generally limited to kw and xw, although some other combinations are occasionally found, though they appear to be tending to obsoletion.wnl,#Consonants
ᨣ᩠ᩅᩣ᩠ᨿ
Other syllable-initial clusters include the combination of ᩉ [U+1A49 TAI THAM LETTER HIGH HA] plus a subjoined low class consonant to make the consonant high class (see highclass). These combinations are not pronounced as multiple consonants.
Final consonants
Northern Thai text commonly renders syllable-final consonants using regular consonant code points (see the example just below), but sometimes special combining characters are used.
ᩑᨠ
Stacking
When regular consonants are used they are commonly subjoined, eg.
ᨠᩣ᩠ᩁ
There are, however, exceptions. For example, when preceded by a subscript vowel a final consonant may be rendered on the baseline, eg.
ᩃᩪᨠ
Northern Thai tends to add sub-base vowels below a consonant stack, whereas Khün typically shifts the vowel to the right of the stack (see fig_kiss).
Positioning of U vowel sign after a stack. In Northern Thai (right) it commonly occurs below the stack, whereas in Khün (left) it tends to be moved to the side.details
ᨧ᩠ᨷᩪ
Due to font design or USE (the Universal Shaping Engine) the characters may have to be typed in an order that departs from the spoken order so that they look as expected. For example, the word in fig_kiss is stored as CCV, whereas it is pronounced CVC.
Combining marks
The following diacritics are sometimes used for syllable-final consonants.
ᩘ [U+1A58 TAI THAM SIGN MAI KANG LAI] can also be used to represent a syllable-final nasal. Click on the name for details. Note that this diacritic has a very different shape in the Khün orthography. Compare ᩅᩘ and ᩅᩘ.
ᩢ [U+1A62 TAI THAM VOWEL SIGN MAI SAT] is commonly used as a vowel, but it also sometimes functions to indicate a final -k sound, eg.
ᨯᩢᩬ
᩺ [U+1A7A TAI THAM SIGN RA HAAM] is used in Northern Thai to silence one or more characters in a word. It is not always clear which sound or sounds are cancelled. Click on the following words to see how the letters map to sounds.
ᨵᨾ᩠ᨾ᩺
ᨼᩥᩃ᩠ᨾ᩺
In Lü it is used as a final n; in Khün it is used as a final r.
Consonant to script mapping
This section maps Northern Thai consonant vowel sounds to common graphemes in the Lanna orthography, where h indicates high class, m is mid class, l is low class, and f indicates a final consonant. Click on a grapheme to find other mentions on this page (links appear at the bottom of the page). Click on the character name to see examples and for detailed descriptions of the character(s) shown.
Sounds listed as 'infrequent' are allophones, or sounds used for foreign words, etc.
As part of a diphthong, this is typically rendered using the subjoined form. See consonant_vowels.
Encoding choices
A number of questions need to be addressed with regards to ordering of characters in composite vowels and stacks. These have been discussed by Unicode experts, but no conclusions have yet been reached. Here we will list some examples.
A number of choices made for this page are enforced by the Hariphunchai font which is used, however other fonts allow different choices.
Order of YA
A first example concerns the order of vowel components that include a subjoined YA. The following produce identical output for the composite vowel pronounced ia in the Payap Lanna, Lamphun, and Hariphunchai fonts (but not in the Noto Sans Tai Tham font).
In this case, the first alternative, which subjoins the YA with the KA and follows it with the MAI SAT vowel sign seems the more intuitive, since the diphthong produced is ia.
However, change the sound to aj and the above logic would lean towards the second of the two following encodings, which also produce identical results.
This is somewhat unusual for Unicode, since it involves an invisible stacker appearing after a vowel mark (there is no other way of producing the right shape for the semivowel j).
Subjoined OA
The following 2 sequences produce identical visual results.
ᨠᩴ᩠ᩋ
kɔː(?)[HIGH KA + MAI KANG + SAKOT + A]
ᨠᩬᩴ
kɔː(?)[HIGH KA + VOWEL SIGN OA BELOW + MAI KANG]
There appears to be some question about which is the appropriate sequence for the composite vowel -ɔː.
Symbols
Logographs
᪠␣᪡␣᪢
The meaning of each of the logographs is shown above. Unicode classes these symbols as punctuation.
Cryptography
᩿
᩿ [U+1A7F TAI THAM COMBINING CRYPTOGRAMMIC DOT] is used singly or multiply beneath letters to give each letter a different value according to some hidden agreement between reader and writer. u,665
Numbers
Digits
᪀␣᪁␣᪂␣᪃␣᪄␣᪅␣᪆␣᪇␣᪈␣᪉᪐␣᪑␣᪒␣᪓␣᪔␣᪕␣᪖␣᪗␣᪘␣᪙
Two sets of digits are in common use: a secular set (Hora) and an ecclesiastical set (Tham). European digits are also found in books. u,665
Text direction
Northern Thai text runs left to right in horizontal lines.
This section brings together information about the following topics:
writing styles;
cursive text;
context-based shaping;
context-based positioning;
baselines, line height, etc.;
font styles;
case & other character transforms.
The orthography has no case distinction, and no special transforms are needed to convert between characters.
Since there are no conjuncts, there is not so much contextual shaping in Tham as in many other Brahmi-descended scripts.
Glyph styles
In addition to the regular differences in shape of glyphs in Northern Thai and Tai Khün, the shapes of certain glyphs in Northern Thai texts may also vary, depending on the region or source.
Regional variation in the shape of subjoined NA is evident in manuscripts from Xishuangbanna (Yunnan Province, China), Keng Tung (Shan State, Myanmar), and Chiangmai (Thailand). (Source: Trager)
By way of a further example, the Payap Lanna and Haripunchai fonts differ in terms of styling, but some glyphs are substantially different. The following table shows glyph shapes for various characters in both fonts.
Hariphunchai
ᩳ
ᩘ
ᩝ
ᩞ
ᨫ
᪬
᪥
᪢
Payap Lanna
ᩳ
ᩘ
ᩝ
ᩞ
ᨫ
᪬
᪥
᪢
Context-based shaping & positioning
Northern Thai text relies on rules to correctly position glyphs and shape them according to the surrounding text.
One major area where this applies is in the use of subjoined forms for consonant stacks (see clusters). Many of the subjoined forms of a letter are substantially different and/or smaller than the normal letter glyph, but the character in memory is the same.
Standard and subjoined forms of the letter MA.
The following is a selection of other examples of contextual shaping and positioning.
Placement of tone marks may involve special shaping and positioning. In some fonts a tone mark is displayed alongside a superscript vowel sign, rather than above it.
Positioning of tone marks next to a superscript vowel in the Hariphunchai font.
A number of code point sequences may be ligated by a font.
Examples of ligated forms for code point sequences.
Font styling & weight
tbd
Graphemes
Grapheme clusters
tbd
Punctuation & inline features
Word boundaries
Spaces separate phrases. There is no separation of individual words.
A new word may start with a subjoined consonant. Stacking is performed across word boundaries. This means that operations such as line-breaking, word highlighting, etc. have to use an orthographic syllable unit which differs from the underlying phonetic syllables.
Phrase & section boundaries
᪨␣᪩␣᪪␣᪫␣?␣!␣᪣␣᪤␣᪥␣᪭␣᪦␣᪬
Northern Thai uses a variety of native punctuation, and only a couple of ASCII code points.
Northern Thai texts use quotation marks around quotations. Of course, due to keyboard design, quotations may also be surrounded by ASCII double and single quote marks.
There are no spaces between words in Northern Thai to serve as line-break opportunities. Lines must be broken at orthographic syllable boundaries. Since the onset consonant of a word or syllable may be subjoined below a previous consonant, and stacks must not be broken, orthgraphic syllable units typically don't match phonetic syllables or words.
In-word line-breaking
In-word line-breaking is a fact of life, because stacks cannot be broken, but no hyphen or other character is used to indicate that a word was broken.
Line-edge rules
As in almost all writing systems, certain punctuation characters should not appear at the end or the start of a line. The Unicode line-break properties help applications decide whether a character should appear at the start or end of a line.
The following list gives examples of typical behaviours for some of the characters used in modern Northern Thai. Context may affect the behaviour of some of these and other characters. Most of the Northern Thai characters, including native punctuation, will prevent a line break before or after, and require morphological analysis to determine break opportunities, in a way similar to a hyphenation algorithm. No break opportunities will be found otherwise. Complex context analysis, often involving dictionary lookup of some form, is required to determine non-emergency line breaks. If such analysis is not available,.
Click/tap on the Bangla characters to show what they are.
“ ‘ ( should not be the last character on a line.
” ’ ) . , ; ! ? । ॥ % should not begin a new line.
Line breaking should not move a danda or double danda to the beginning of a new line even if they are preceded by a space character.
Text alignment & justification
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Text spacing
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Baselines, line height, etc.
Northern Thai uses the so-called 'alphabetic' baseline, which is the same as for Latin and many other scripts.
Northern Thai places vowel and tone marks above base characters, one above the other, and can also add combining characters below the line. It also stacks characters, though stacks are usually limited in height. The complexity of the text means that the vertical resolution needed for clearly readable Northern Thai text is higher than for English, or most Latin text. In addition,
To give an approximate idea, fig_baselines compares Latin and Northern Thai glyphs from the Payap Lanna font. The basic height of Northern Thai letters is typically around the Latin x-height, however extenders and combining marks reach well beyond the Latin ascenders and descenders, creating a need for larger line spacing.
Font metrics for Latin text compared with Northern Thai glyphs in the Payap Lanna font.
Counters, lists, etc.
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Page & book layout
This section is for any features that are specific to Northern Thai and that relate to the following topics:
general page layout & progression;
grids & tables;
notes, footnotes, etc;
forms & user interaction;
page numbering, running headers, etc.
References
Acknowledgements
Many thanks are due to Richard Wordingham and Patrick Chew for reviewing the initial draft of this material and sending suggestions.
