For webpages on this site, I used the following HTML code to center a div on the pages:
<div id="header" align="center">
That didn't produce any error messages when I used the HTML 4.01 document type (doctype) declaration below as the first lines in the HTML file when I checked the page for errors using the W3C Markup Validation Service.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
However, when I wanted to convert the pages to make them valid for HTML 5 and put <!DOCTYPE html> as the first line in the file, instead, I saw the following error message reported by the validation service:
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