NR connects fraction words with superlatives:

               +------L----+
               |    +--NR--+
	       |    |      |
	It is the third biggest city in China

Superlative adjectives connect back to the previous determiner,
rather than connecting forward to the noun like most adjectives.
See "L".

NR is also used in time idioms like "The second time I saw her,
she was walking in the park". See "TT".