Sentence:  On Fridays , the day when many Persians relax with poetry , talk , and a samovar , people do not , it <WSD>is</WSD> true , stream into Chehel Sotun - a pavilion and garden built by Shah Abbas 2 , in the seventeenth century - but they do retire into hundreds of pavilions throughout the city and up the river valley , which are smaller , more humble copies of the former . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)