Valid XHTML - blog post

One of the problem areas I had to address before I could produce valid XHTML was the contents of my posts. I thought I did it all right until i started validating just to discover that the structure was not what I had expected. I had expected that the posts would be embedded in a <div> tag but it isn't it's in a <p> tag, which limits that valid child elements, as can be seen from this overview of the paragraph tag. I produce my postings in the Edit Html mode but the problem would also be there if I used Compose mode, and in fact it's only with raw XHTML that I'll produce valid markup. In the compose mode one can make an ordered list with the normal <ul; and <li> tags but they are not allowed inside the <p> tag, so I've decided to drop them for now. Also <blockquote> and headlines with ex. <h2> are not allowed and not the lease <pre>. To overcome this I've added my own css classes to be used with <span>

/* custom classes due to limitation in markup allowed in 
 tags*/
tiny { font-size:78%; }
.small { font-size:85%; }
.normal { font-size:100%; }
.large { font-size:130%; }
.huge { font-size:180%; }

.h2 { font-size:130%; 
      font-weight: bold; }
.pre { color: black; 
       white-space: pre; 
       background-color:lightgrey; 
       display: block; }
.blockquote { margin:1em 20px; }

Here'a an example using the font sizes:
* This is Tiny text
* This is Small text
* This is Normal text
* This is Large text
* This is Huge text