docs: def are_diphtong(tokenA, tokenB):
  	"""
  	Check (naively) whether the two tokens can form a diphtong. This would be a
  	sequence of vowels of which no more than one is syllabic. Vowel sequences
  	connected with a tie bar would already be handled in tokenise_word, so are
  	not checked for here.
  
  	Users who want more sophisticated diphtong detection should instead write
  	their own function and do something like::
  
  		tokenise(string, diphtong=False, merge=user_func)
  
  	Helper for tokenise(string, ..).
  	"""
  	is_short = lambda token: '◌̯'[1] in token
  	subtokens = []
  
  	for char in tokenA+tokenB:
  		if ipa.is_vowel(char):
  			subtokens.append(char)
  		elif ipa.is_diacritic(char) or ipa.is_length(char):
  			if subtokens:
  				subtokens[-1] += char
  			else:
  				break
  		else:
  			break
  	else:
  		if len([x for x in subtokens if not is_short(x)]) < 2:
  			return True
  
  	return False