Dictionary line breaking: Thai, Lao, Khmer and Burmese

These scripts put no spaces between words, so no rule can say where a line may end: PeachPDF looks the words up in a word list (ICU's dictionaries) and wraps between them, never inside a syllable. The same Thai (then Lao, then Khmer) paragraph is set in three widths: the words move to the next line whole, whatever the width. The lang attribute does not matter, the script does. The Khmer paragraph also shows real coeng/subjoined-consonant shaping: a subjoined consonant stacks below its base rather than rendering as a separate nominal glyph.

The words as blocks: Burmese

The same idea in the line breaking test font, where every character (a vowel sign or tone mark too) is a square one em wide, and each box holds six of them: a word that does not fit the rest of the line starts the next one, and a syllable is never cut. Burmese is shown this way only (PeachPDF does not yet shape its own stacked/subscript consonants - Khmer's own equivalent is shown above, in real glyphs).