pub const UNPRINTABLE_SUBSTITUTE: char = '?';Expand description
What a character the card font cannot draw is printed as.
A dropped glyph is INVISIBLE: printpdf emits nothing at all for a codepoint the embedded
font has no entry for. Liberation Sans covers Latin, Latin-1, Cyrillic, Greek and the
usual punctuation, and nothing else — so a card renamed “射撃カード 308” used to print a
header reading “308”, and an all-Arabic or all-Thai name printed a BLANK header, with no
error and a normal byte length. A visible stand-in at least tells the shooter that
something stood there; unprintable_chars reports WHAT, so the caller can warn before
the paper leaves the printer.