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import unicode from 'unicode-properties';
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/**
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* This class is used when GPOS does not define 'mark' or 'mkmk' features
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* for positioning marks relative to base glyphs. It uses the unicode
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* combining class property to position marks.
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*
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* Based on code from Harfbuzz, thanks!
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* https://github.com/behdad/harfbuzz/blob/master/src/hb-ot-shape-fallback.cc
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*/
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export default class UnicodeLayoutEngine {
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constructor(font) {
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this.font = font;
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}
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positionGlyphs(glyphs, positions) {
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// find each base + mark cluster, and position the marks relative to the base
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let clusterStart = 0;
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let clusterEnd = 0;
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for (let index = 0; index < glyphs.length; index++) {
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let glyph = glyphs[index];
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if (glyph.isMark) { // TODO: handle ligatures
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clusterEnd = index;
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} else {
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if (clusterStart !== clusterEnd) {
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this.positionCluster(glyphs, positions, clusterStart, clusterEnd);
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}
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clusterStart = clusterEnd = index;
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}
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}
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if (clusterStart !== clusterEnd) {
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this.positionCluster(glyphs, positions, clusterStart, clusterEnd);
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}
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return positions;
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}
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positionCluster(glyphs, positions, clusterStart, clusterEnd) {
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let base = glyphs[clusterStart];
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let baseBox = base.cbox.copy();
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// adjust bounding box for ligature glyphs
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if (base.codePoints.length > 1) {
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// LTR. TODO: RTL support.
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baseBox.minX += ((base.codePoints.length - 1) * baseBox.width) / base.codePoints.length;
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}
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let xOffset = -positions[clusterStart].xAdvance;
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let yOffset = 0;
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let yGap = this.font.unitsPerEm / 16;
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// position each of the mark glyphs relative to the base glyph
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for (let index = clusterStart + 1; index <= clusterEnd; index++) {
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let mark = glyphs[index];
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let markBox = mark.cbox;
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let position = positions[index];
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let combiningClass = this.getCombiningClass(mark.codePoints[0]);
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if (combiningClass !== 'Not_Reordered') {
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position.xOffset = position.yOffset = 0;
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// x positioning
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switch (combiningClass) {
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case 'Double_Above':
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case 'Double_Below':
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// LTR. TODO: RTL support.
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position.xOffset += baseBox.minX - markBox.width / 2 - markBox.minX;
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break;
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case 'Attached_Below_Left':
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case 'Below_Left':
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case 'Above_Left':
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// left align
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position.xOffset += baseBox.minX - markBox.minX;
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break;
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case 'Attached_Above_Right':
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case 'Below_Right':
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case 'Above_Right':
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// right align
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position.xOffset += baseBox.maxX - markBox.width - markBox.minX;
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break;
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default: // Attached_Below, Attached_Above, Below, Above, other
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// center align
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position.xOffset += baseBox.minX + (baseBox.width - markBox.width) / 2 - markBox.minX;
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}
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// y positioning
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switch (combiningClass) {
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case 'Double_Below':
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case 'Below_Left':
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case 'Below':
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case 'Below_Right':
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case 'Attached_Below_Left':
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case 'Attached_Below':
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// add a small gap between the glyphs if they are not attached
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if (combiningClass === 'Attached_Below_Left' || combiningClass === 'Attached_Below') {
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baseBox.minY += yGap;
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}
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position.yOffset = -baseBox.minY - markBox.maxY;
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baseBox.minY += markBox.height;
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break;
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case 'Double_Above':
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case 'Above_Left':
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case 'Above':
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case 'Above_Right':
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case 'Attached_Above':
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case 'Attached_Above_Right':
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// add a small gap between the glyphs if they are not attached
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if (combiningClass === 'Attached_Above' || combiningClass === 'Attached_Above_Right') {
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baseBox.maxY += yGap;
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}
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position.yOffset = baseBox.maxY - markBox.minY;
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baseBox.maxY += markBox.height;
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break;
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}
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position.xAdvance = position.yAdvance = 0;
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position.xOffset += xOffset;
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position.yOffset += yOffset;
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} else {
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xOffset -= position.xAdvance;
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yOffset -= position.yAdvance;
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}
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}
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return;
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}
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getCombiningClass(codePoint) {
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let combiningClass = unicode.getCombiningClass(codePoint);
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// Thai / Lao need some per-character work
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if ((codePoint & ~0xff) === 0x0e00) {
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if (combiningClass === 'Not_Reordered') {
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switch (codePoint) {
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case 0x0e31:
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case 0x0e34:
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case 0x0e35:
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case 0x0e36:
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case 0x0e37:
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case 0x0e47:
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case 0x0e4c:
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case 0x0e3d:
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case 0x0e4e:
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return 'Above_Right';
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case 0x0eb1:
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case 0x0eb4:
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case 0x0eb5:
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case 0x0eb6:
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case 0x0eb7:
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case 0x0ebb:
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case 0x0ecc:
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case 0x0ecd:
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return 'Above';
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case 0x0ebc:
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return 'Below';
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}
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} else if (codePoint === 0x0e3a) { // virama
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return 'Below_Right';
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}
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}
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switch (combiningClass) {
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// Hebrew
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case 'CCC10': // sheva
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case 'CCC11': // hataf segol
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case 'CCC12': // hataf patah
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case 'CCC13': // hataf qamats
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case 'CCC14': // hiriq
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case 'CCC15': // tsere
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case 'CCC16': // segol
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case 'CCC17': // patah
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case 'CCC18': // qamats
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case 'CCC20': // qubuts
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case 'CCC22': // meteg
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return 'Below';
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case 'CCC23': // rafe
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return 'Attached_Above';
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case 'CCC24': // shin dot
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return 'Above_Right';
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case 'CCC25': // sin dot
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case 'CCC19': // holam
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return 'Above_Left';
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case 'CCC26': // point varika
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return 'Above';
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case 'CCC21': // dagesh
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break;
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// Arabic and Syriac
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case 'CCC27': // fathatan
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case 'CCC28': // dammatan
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case 'CCC30': // fatha
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case 'CCC31': // damma
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case 'CCC33': // shadda
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case 'CCC34': // sukun
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case 'CCC35': // superscript alef
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case 'CCC36': // superscript alaph
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return 'Above';
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case 'CCC29': // kasratan
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case 'CCC32': // kasra
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return 'Below';
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// Thai
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case 'CCC103': // sara u / sara uu
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return 'Below_Right';
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case 'CCC107': // mai
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return 'Above_Right';
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// Lao
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case 'CCC118': // sign u / sign uu
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return 'Below';
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case 'CCC122': // mai
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return 'Above';
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// Tibetan
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case 'CCC129': // sign aa
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case 'CCC132': // sign u
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return 'Below';
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case 'CCC130': // sign i
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return 'Above';
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}
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return combiningClass;
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}
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}
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