Walt Whitman wrote a lot. Not only did he write a boat load of poetry; he also kept revising his work and issuing it in new editions throughout his life. That's what he did with his most famous book, the poetry collection Leaves of Grass.
The Walt Whitman Archive is another big project of the Digital Humanities. It's a huge repository of Whitman's work, and it includes all the published editions of Leaves of Grass. What's so useful about having all of these editions in one place on the web? Well, this archive allows Digital Humanists to compare and contrast different versions and revisions of Whitman's work.
Whitman grouped a number of his poems in the collection under the heading "Leaves of Grass" (yup, the same as the title of the book). In each edition of the book, he revised and added to this cluster of poems. Let's look at the first two poems in this cluster in two different editions—the 1867 edition and the 1871-72 edition: