Important rules regarding attributes in XHTML 1.0:

Attributes must be in lower case.
BAD
<input type="TEXT" />
GOOD
<input type="text" />

Attribute values must be quoted.
BAD
<img src=picture.gif />
<div class=my_div>
GOOD
<img src="picture.gif" />
<div class="my_div">

Attribute values must be written in full, no minimization allowed.
BAD
<input readonly />
<option selected>
GOOD
<input readonly="readonly" />
<option selected="selected">

 

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