metric for block coverage

[J. S. Choi via Unicode]

Better heuristics of the coverage by a font of a human script sound useful, but don’t the standards discourage using codepoint blocks for determining whether a character belongs to the repertoire of a human language or script? Although the specification authors try to arrange characters into codepoint blocks as logically as they can, codepoint blocks are, most of all, artifacts of Unicode’s own patchwork history. Additional information, such as script information or ICU data, is often required to correctly determine a script’s repertoire of essential characters. See also https://www.unicode.org/reports/tr18/#Character_Blocks and https://www.unicode.org/faq/blocks_ranges.html#16.

Another thing to point out is that correct rendering of script-essential combined characters is another important part of font quality. This would be difficult to evaluate only with a heuristic based on codepoint blocks. 

J. S. Choi
Saint Louis University
School of Medicine 
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