(1) The spelling rules for "y" and "w" in pinyin are described. "Y" is used before vowels like "i" and "u" when there is no initial consonant. "W" is added before the final "u" when it acts as a syllable. (2) Tone marks are written above the main vowel of each syllable, with exceptions for "iu" and "ui" where the tone mark goes on the second vowel. (3) An apostrophe is used to separate syllables with connecting vowels to avoid confusion, such as in "Xī’ān" and "nǚ’ér". It can also be used for syll