"Sonnets from the Portuguese" is a collection of 44 love sonnets that Elizabeth Barrett Browning (6 March 1806 - 29 June 1861) wrote in 1845-46 and first published in 1850. As with Richard and Patty's efforts to shield the true identities of the authors of their letters, Elizabeth Barrett Browning attempted to shield the true identity of her collection's author by suggesting that they were translations of Portuguese sonnets, hence the title. One of the more famous passages from these sonnets begins with "How do I love thee? Let me count the ways."
There are similarities between the plot here and earlier movie plots from The Shop Around the Corner (1940) and In the Good Old Summertime (1949), wherein two people are romantically entwined by the anonymous letters they write to one another while simultaneously disdaining each other in their daily encounters with one another.
Lancelot is a fictional character in the tales of knights of the round in King Arthur's court at Camelot. Guinevere is King Arthur's queen. As with Richard and Patty's secret romantic dalliances, Lancelot and Guinevere also carried on an affair, which they attempted to keep secret from Arthur.
The book Patty carries with her to rendezvous with her pen pal is a book of poems by Elizabeth Barrett Browning (6 March 1806 - 29 June 1861), the same author for the book Judy Garland carries with her when she attempts to rendezvous with her pen pal in In the Good Old Summertime (1949).