The big IDEs should show the code always formatted, aligned with visual line breaks as the reader want it, and not the writer intended. Apple Script Editor did it like that. That was impressing.
With a non monospace font programming is easier because typos are easier to find because of different width:
<div><span class="highlight">M</span></div>
<div><span class="highlight">M</span></div>
<div><span class="highlight">M</span></div>
<div><spam class="highlight">M</spam></div>
<div><span class="highlight">M</span></div>
Also bold, italic and serif helps to differentiate different types of code.
