So I think the answer to this is a custom plugin/Kirbytag, but I’m not sure how to put it together and use it. I’m looking to duplicate Hugo’s shortcode functionality in Kirby, such that I can enter the tag in the post content and have it expanded behind the scenes. As an example from my Tufte theme, the epigraph code:
<div class="epigraph">
<blockquote>
{{ $t := .Get "type" }}
{{ if eq $t "compact" }}{{ .Inner | markdownify }}{{ else }}<p>{{ .Inner | markdownify }}</p>{{ end }}
{{ if .IsNamedParams }}
<footer>
{{ with .Get "pre" }}{{ . }}{{ end }}
{{ with .Get "link" | safeURL | markdownify }}<a href={{ . }} target="_blank" rel="noopener">{{ end }}
{{ with .Get "cite" }}<cite>{{ . }}</cite>{{ end }}
{{ if .Get "link"}}</a>{{ end }}
{{ with .Get "post" }}{{ . }}{{ end }}
</footer>
{{ end }}
</blockquote>
</div>
This is what gets produced from the following shortcode syntax within the post itself:
{{< epigraph pre="Person's Name" cite="Site Name" link="//example.com/link/" >}}blockquote text goes here{{< /epigraph >}}
Where and how do I create the Kirby equivalent for this, and deploy it within blog post content? I think once I’ve gotten one of these down, the rest should be straightforward.
Forgive my still noob-ness. 
(Edit: And yes, there’s a higher than zero percent chance I’m planning on porting Tufte to Kirby.)