My first impression is that conditionals are not supported under Sigil regex...but I have to admit, my regex-fu is not
that strong... I'll be interest to see what the true experts have to say.
I would recommend
not using styles within your html, you should use CSS files instead. <span style="font-size: 1.0em">XXXXX</span> is pure bloat.
"Structure in the HTML and style in the CSS"
Code:
CSS:
p {font-size:1em}
p.double {font-size:2em}
HTML:
<p>Normal paragraph.</p>
<p>Normal paragraph.</p>
<p>Normal paragraph.</p>
<p class="double">Double font-size paragraph.</p>
<p>Normal paragraph.</p>
<p>Normal paragraph.</p>