generate
Create an object of the appropriate size, whose descriptor is an instance of TwentyOneBitStringDescriptor. This can store any Unicode character, including those from the Supplemental Planes. Run the generator for each position in ascending order to produce the code points with which to populate the string.
Return
The new Avail string.
Parameters
size
The size of twenty-one-bit string to create.
generator
A generator to provide code points to store.