I have not, however, been producing valid xhtml. To do so, I need to remember to url encode my links, and also, apparently, a "blockquote" cannot appear inside a paragraph. I have to end the paragraph, start the blockquote, and then start a paragraph after ending the blockquote. The logic appears to be that the blockquote can contain paragraphs, so a paragraph cannot contain a blockquote. That sort of makes sense, I guess, but it is logically inconsistent, as, when writing, I generally continue the previous paragraph after the blockquote. This follows from years of highschool and college writing. Still, since in web pages I use a block format, not indenting my paragraphs, it visually produces the correct output this way, so it matters little.
