New in version 2.0.
True when expr is a LilyPond rest string:
abjad> resttools.is_lilypond_rest_string('r4.. * 1/2')
True
Otherwise false:
abjad> resttools.is_lilypond_rest_string('text')
False
The regex ^(r|R)\s*(1|2|4|8|16|32|64|128|\breve|\longa|\maxima)\s*(\.*)\s*(\*\s*(\d+(/\d+)?))?$ underlies this predicate.
Return boolean.