Some older browsers such as Netscape 3.0 and Internet Explorer 4.0 do have varying degrees of difficulty with XHTML constructs such as empty-element tags. For example, Netscape 3 places two horizontal lines when it sees <hr></hr> and none at all when it sees <hr/>. It is unwise to use the full panoply of XML syntax when serving XHTML to browsers. In particular, here are my suggestions.
Include at least one space before the /> in an empty-element tag.
Do not use CDATA sections.
Do not use processing instructions such as xml-stylesheet, especially in the document prolog.
Do not use character references such as đ or ψ.
Do not use entity references that were not available in HTML 1.0 such as ” and τ.
Do not include ...