However there's something important to notice when closing tas which contains unclosed tags.
It concerns CSS styles. If you define in a CSS file :

CODE
body { font-color: black; }
b    { font-color: green; }
b u  { font-color: blue; }
u    { font-color: red; }


When interpreted, the code would render as :
CODE
<b><u>Blue,  Bold, Underlined</b>Black, Underlined</u>
<u><b>Green, Bold, Underlined</b>Red,   Underlined</u>


When closing a tag which contains an unclosed tag, it do not end the main definition of the tag (bold, underlined) bu do end the definition of the CSS style (font-color).