Always use & in place of & when writing URLs in HTML.
Example of invalid ampersand for URL in HTML:
<a href="test.php?var1=3&var2=6&var3=10">...</a>The correct usage:
<a href="test.php?var1=3&var2=6&var3=10">...</a>To validate for markup, please use W3C Markup Validator.
