A bare string
HTML5 does allow CDATA sections in SVG
A tag
A
tag that supposedly has contents.
AT&T
This numeric entity is missing the final semicolon:
, that attribute value was closed by the subsequent tag
a
This document contains (do you see it?)
This document ends with That attribute value was bogus
The doctype is invalid because it contains extra whitespace
That boolean attribute had no value
Here's a nonexistent entity: &#foo; (do you see it?)
This document ends before the entity finishes: >

Paragraphs shouldn't contain block display elements, but this one does:

you see?

Multiple values for the same attribute.
Here's a table
This tag contains nothing but whitespace:

This p tag is cut off by

the end of the blockquote tag
Here's a nested table:
foo
This table contains bare markup
\n
This document contains a surprise doctype
Mixed case tags are folded to lowercase
Tag name contains Unicode characters
Attribute name contains Unicode characters