metric for block coverage

[James Kass via Unicode]

Adam Borowski wrote,

> It's only a single bit without a meaning beyond "range is considered
> functional".  No "basic coverage" vs "good coverage" vs "full coverage".
> ...
> These codepoints can then be grouped by block -- but interpreting such lists
> is what's unobvious.

Compare the number of glyphs in the range with the number of assigned
characters in the range.  Older fonts would lack  anything added to
The Standard after the font was made.

+1 if the font has any glyphs in the range
+1 if the font has a good portion of glyphs in the range
+1 if the font has all the glyphs in the range
+1 if the font has OpenType tables covering the script
+1 if the script has 1 language tag in addition to 'dflt' tag
+1 if the script has 2 language tags in addition to 'dflt' tag
...

And for a "good portion of glyphs in the range", possibly the number
of characters in the range which were assigned as of Unicode 3.0 would
indicate a more-or-less "basic coverage" of that range.