What Does TEI Markup Look Like?

The following example is from The Walt Whitman Archive. It shows a portion of the markup written to create a facsimile of the original manuscript for Whitman's poem "The Argument."
"The Argument" original manuscript (1890 or 1891)
As you can see in the TEI facsimile below, the Archive seeks to replicate the edits made in the manuscript as well as the layout of the text:
The TEI markup below looks very different from the facsimile but, if you look closely, you can probably understand some of what the markup is doing.
<text type="manuscript">
<pb facs="loc.00001.001.jpg" xml:id="leaf001r" type="recto"/>
<lg type="poem">
<head rend="underline" type="main-authorial">
<del rend="overstrike" seq="1">an</del>
<add place="supralinear" rend="insertion" seq="2">
<del rend="overstrike">unsolv'd</del>
<del rend="overstrike">The</del>
<add place="supralinear" rend="insertion">
<del rend="overstrike">Coming in,</del>
<del rend="overwrite" seq="1">a</del>
<add place="over" rend="overwrite" seq="2">A</add>
group of
little children, and their
ways and chatter, flow
<add place="inline" rend="unmarked">in, </add>
<del rend="overstrike">
<add place="supralinear" rend="unmarked">upon me</add>
<add place="supralinear" rend="insertion">welcome </add>
rippling water o'er my
<add place="supralinear" rend="insertion">nerves and </add>
<signed>Walt Whitman</signed>
<pb facs="loc.00001.002.jpg" xml:id="leaf001v" type="verso"/>