First: thanx 4 ur reply...
The quote is showing that when u analyze a literary text u should:
"take into consideration other 19th century poetry, to understand the events that inspired this poem, to understand Browning's background, etc."
BUT one of the structuralism principles is:
Structuralists dismiss the importance of the author & any historical or literary period. 
Also, i couldn't apply the idea of Mytheme -one of Structuralism principles- on "My Last Duchess" !! 
thanx 4 ur help again ....