Editing Tibetan script (section)

===Consonant clusters===
[[File:Tibetan syllable structure.svg|thumb|400px|Components of a Tibetan syllable]]

[[File:Tibetan map of the Kizil Caves (13th entury CE).jpg|thumb|Tibetan map of the [[Kizil Caves]], [[Tarim Basin]]. 13th century CE]]
One aspect of the Tibetan script is that the consonants can be written either as radicals or they can be written in other forms, such as [[subscript and superscript]] forming [[consonant cluster]]s.

To understand how this works, one can look at the radical {{bo-textonly|ཀ}} /ka/ and see what happens when it becomes {{bo-textonly|ཀྲ}} /kra/ or {{bo-textonly|རྐ}} /rka/ (pronounced /ka/). In both cases, the symbol for {{bo-textonly|ཀ}} /ka/ is used, but when the {{bo-textonly|ར}} /ra/ is in the middle of the consonant and vowel, it is added as a subscript.  On the other hand, when the {{bo-textonly|ར}} /ra/ comes before the consonant and vowel, it is added as a superscript.<ref name="daniels" /> {{bo-textonly|ར}} /ra/ actually changes form when it is above most other consonants, thus {{bo-textonly|རྐ}} rka.  However, an exception to this is the cluster {{bo-textonly|རྙ}} /ɲa/.  Similarly, the consonants {{bo-textonly|ར}} /ra/, and {{bo-textonly|ཡ}} /ja/ change form when they are beneath other consonants, thus {{bo-textonly|ཀྲ}} /ʈ ~ ʈʂa/; {{bo-textonly|ཀྱ}} /ca/.

Besides being written as subscripts and superscripts, some consonants can also be placed in prescript, postscript, or post-postscript positions. For instance, the consonants {{bo-textonly|ག}} /kʰa/, {{bo-textonly|ད}} /tʰa/, {{bo-textonly|བ}} /pʰa/, {{bo-textonly|མ}} /ma/ and {{bo-textonly|འ}} /a/ can be used in the prescript position to the left of other radicals, while the position after a radical (the postscript position), can be held by the ten consonants {{bo-textonly|ག}} /kʰa/, {{bo-textonly|ན}} /na/, {{bo-textonly|བ}} /pʰa/, {{bo-textonly|ད}} /tʰa/, {{bo-textonly|མ}} /ma/, {{bo-textonly|འ}} /a/, {{bo-textonly|ར}} /ra/, {{bo-textonly|ང}} /ŋa/, {{bo-textonly|ས}} /sa/, and {{bo-textonly|ལ}} /la/. The third position, the post-postscript position is solely for the consonants {{bo-textonly|ད}} /tʰa/ and {{bo-textonly|ས}} /sa/.<ref name="daniels" />

====Head letters====
The head ({{bo-textonly|མགོ}} in Tibetan, Wylie: ''mgo'') letter, or superscript, position above a radical is reserved for the consonants {{bo-textonly|ར}} /ra/, {{bo-textonly|ལ}} /la/, and {{bo-textonly|ས}} /sa/.

*When {{bo-textonly|ར}} /ra/, {{bo-textonly|ལ}} /la/, and {{bo-textonly|ས}} /sa/ are in superscript position with {{bo-textonly|ཀ}} /ka/, {{bo-textonly|ཅ}} /t͡ʃa/, {{bo-textonly|ཏ}} /ta/, {{bo-textonly|པ}} /pa/ and {{bo-textonly|ཙ}} /t͡sa/, there are no changes to their sounds in Lhasa Tibetan, for example:
**{{bo-textonly|རྐ}} /ka/, {{bo-textonly|རྟ}} /ta/, {{bo-textonly|རྤ}} /pa/, {{bo-textonly|རྩ}} /t͡sa/
**{{bo-textonly|ལྐ}} /ka/, {{bo-textonly|ལྕ}} /t͡ʃa/, {{bo-textonly|ལྟ}} /ta/, {{bo-textonly|ལྤ}} /pa/, 
**{{bo-textonly|སྐ}} /ka/, {{bo-textonly|སྟ}} /ta/, {{bo-textonly|སྤ}} /pa/, {{bo-textonly|སྩ}} /t͡sa/
*When {{bo-textonly|ར}} /ra/, {{bo-textonly|ལ}} /la/, and {{bo-textonly|ས}} /sa/ are in superscript position with {{bo-textonly|ག}} /kʰa/, {{bo-textonly|ཇ}} /t͡ʃʰa/, {{bo-textonly|ད}} /tʰa/, {{bo-textonly|བ}} /pʰa/ and {{bo-textonly|ཛ}} /t͡sʰa/, they lose their aspiration and become voiced in Lhasa Tibetan, for example:
**{{bo-textonly|རྒ}} /ga/, {{bo-textonly|རྗ}} /d͡ʒa/, {{bo-textonly|རྡ}} /da/, {{bo-textonly|རྦ}} /ba/, {{bo-textonly|རྫ}} /dza/
**{{bo-textonly|ལྒ}} /ga/, {{bo-textonly|ལྗ}} /d͡ʒa/, {{bo-textonly|ལྡ}} /da/, {{bo-textonly|ལྦ}} /ba/, 
**{{bo-textonly|སྒ}} /ga/, {{bo-textonly|སྡ}} /da/, {{bo-textonly|སྦ}} /ba/
*When {{bo-textonly|ར}} /ra/, {{bo-textonly|ལ}} /la/, and {{bo-textonly|ས}} /sa/ are in superscript position with the nasal consonants {{bo-textonly|ང}} /ŋa/, {{bo-textonly|ཉ}} /ɲya/, {{bo-textonly|ན}} /na/ and {{bo-textonly|མ}} /ma/, they receive a high tone in Lhasa Tibetan, for example:
**{{bo-textonly|རྔ}} /ŋa/, {{bo-textonly|རྙ}} /ɲa/, {{bo-textonly|རྣ}} /na/, {{bo-textonly|རྨ}} /ma/
**{{bo-textonly|ལྔ}} /ŋa/
**{{bo-textonly|སྔ}} /ŋa/, {{bo-textonly|སྙ}} /ɲa/, {{bo-textonly|སྣ}} /na/, {{bo-textonly|སྨ}} /ma/
*When {{bo-textonly|ལ}} /la/ is in superscript position with {{bo-textonly|ཧ}} /ha/, it becomes a [[Lateral consonant#Approximants|voiceless alveolar lateral approximant]] in Lhasa Tibetan:
**{{bo-textonly|ལྷ}} /l̥a/,

====Sub-joined letters====
The subscript position under a radical can only be occupied by the consonants {{bo-textonly|ཡ}} /ja/, {{bo-textonly|ར}} /ra/, {{bo-textonly|ལ}} /la/, and {{bo-textonly|ཝ}} /wa/.  In this position they are described as {{bo-textonly|བཏགས}} (Wylie: ''btags'', IPA: /taʔ/), in Tibetan meaning "hung on/affixed/appended", for example {{bo-textonly|བ་ཡ་བཏགས་བྱ}} (IPA: /pʰa.ja.taʔ.t͡ʃʰa/), except for {{bo-textonly|ཝ}}, which is simply read as it usually is and has no effect on the pronunciation of the consonant to which it is subjoined, for example {{bo-textonly|ཀ་ཝ་ཟུར་ཀྭ}} (IPA: /ka.wa.suː.ka/).