The way that Sigil Clips works is you highlight text, and then you apply the Clip.
Your highlighted text will be grouped into:
\1
So let's say you highlight:
Code:
This is text I |want in italics|.
Clip: <i>\1</i>
Code:
This is text I <i>want in italics</i>.
Clips are designed more as a one-button-push for redundant stuff (like pasting in template code for a figure with caption, etc. etc.)
Like I created this Sigil Clip for myself:
Code:
<div class="chart">
<div class="single-chart">
<div class="chart-title"></div>
<div class="image"></div>
<div class="chart-caption"></div>
</div>
</div>
and then I can easily just insert the needed info/images.
To do more advanced Search/Replace using Regex, you use
Tools > Saved Searches.