shaper

In HarfBuzz, a shaper is a handler for a specific script shaping model. HarfBuzz implements separate shapers for Indic, Arabic, Thai and Lao, Khmer, Myanmar, Tibetan, Hangul, Hebrew, the Universal Shaping Engine (USE), and a default shaper for non-complex scripts.

cluster

In text shaping, a cluster is a sequence of codepoints that must be handled as an indivisible unit. Clusters can include codepoint sequences that form a ligature or base-and-mark sequences. Tracking and preserving clusters is important when shaping operations might separate or reorder codepoints.

HarfBuzz provides three cluster levels that implement different approaches to the problem of preserving clusters during shaping operations.