New in version 2.0.
True when expr equals a nonnegative integer:
abjad> from abjad.tools import mathtools
abjad> mathtools.is_nonnegative_integer(99)
True
abjad> mathtools.is_nonnegative_integer(0)
True
Otherwise false:
abjad> mathtools.is_nonnegative_integer(-1)
False
Return boolean.