Returns .true if the receiving string contains the
other string.
It returns .false if other is
the null string or is not found within the receiving string.
By default, the search starts at the first character of the
receiving string and continues to the end.
You can override this by specifying start,
the point at which the search starts, and length,
the bounding limit for the search.
If specified, start must be a positive
whole number and length must be
a non-negative whole number.
