That's why I hedged a bit. SVG is certainly less readable, but it can be human readable if not aggressively minimized.
I've both created and modified SVG documents by hand with a text editor, and also view-sourced SVGs to see how they work.
The only thing that is especially unreadable are the long strings of coordinates that make up paths, and even those can be manageable with comments. No one does complex paths by hand, but the rest is colors, shapes, transforms -- all things you can read and may want to modify.
I've both created and modified SVG documents by hand with a text editor, and also view-sourced SVGs to see how they work.
The only thing that is especially unreadable are the long strings of coordinates that make up paths, and even those can be manageable with comments. No one does complex paths by hand, but the rest is colors, shapes, transforms -- all things you can read and may want to modify.