docs: def getCommon(self, st1, st2):
  		"""
  		getCommon() returns the length of the longest common substring
  		of both arguments, starting at the beginning of both.
  		"""
  		fl = len(st1)
  		shorter = len(st2)
  		if fl < shorter:
  			shorter = fl
  
  		i = 0
  		while i < shorter:
  			if st1[i] != st2[i]:
  				break
  			i += 1
  		return i