How To Capture First Paragraph ?

Folks,

Say I fetched a page:

file_get_html($url);

Now need to grab the first whole paragraph onto another $par, then from that $par, scrape 255 chars. Then dump that to index (MySql dB) as link’s description.
Ok, not gonna get you to write the whole code but tell me atleast which PHP function grabs paragraphs in an HTML file ?
I’ll scrape whole page’s all paragraphs one by one onto an array then target array POS 0 and count that as first paragraph. Then scrape 255 chars out of that 0 key array.
Also let me know how to limit scraping characters to 255 chars only. Which PHP function to look into.