isAsciiWhitespace
The whitespace every block and inline rule is defined in: ASCII only, so a no-break space is ordinary text and does not separate a heading's hashes from its title. Emphasis flanking is the one rule keyed on Unicode whitespace, as CommonMark 0.31.2 defines it.
Return
whether the character is one of space, tab, line feed, vertical tab, form feed or carriage return
Parameters
char
character to classify