That all depends really for example if you had two different lines of coding.
<img src="apngImage.png" border="0" />
and
if(someCondition){
echo "<img src=\"apngImage.png\" border=\"0\" />"://or a better way
echo "<img src='apngImage.png' border='0' />";//use single quote inside double to eliminate escape backslashes
Both do the same thing, except one in HTML always shows whereas the PHP version generates the HTML but only when a condition is met, other than that they are the same.