--- title: Passthrough render hooks linkTitle: Passthrough description: Create passthrough render hook templates to override the rendering of text snippets captured by the Goldmark Passthrough extension. categories: [] keywords: [] --- ## Overview Hugo uses [Goldmark][] to render Markdown to HTML. Goldmark supports custom extensions to extend its core functionality. The [Passthrough][] extension captures and preserves raw Markdown within delimited snippets of text, including the delimiters themselves. These are known as _passthrough elements_. Depending on your choice of delimiters, Hugo will classify a passthrough element as either _block_ or _inline_. Consider this contrived example: ```md {file="content/example.md"} This is a \[block\] passthrough element with opening and closing block delimiters. This is an \(inline\) passthrough element with opening and closing inline delimiters. ``` Update your project configuration to enable the Passthrough extension and define opening and closing delimiters for each passthrough element type, either `block` or `inline`. For example: {{< code-toggle file=hugo >}} [markup.goldmark.extensions.passthrough] enable = true [markup.goldmark.extensions.passthrough.delimiters] block = [['\[', '\]'], ['$$', '$$']] inline = [['\(', '\)']] {{< /code-toggle >}} In the example above there are two sets of `block` delimiters. You may use either one in your Markdown. The Passthrough extension is often used in conjunction with the MathJax or KaTeX display engine to render [mathematical expressions][] written in the LaTeX markup language. To enable custom rendering of passthrough elements, create a passthrough render hook. ## Context Passthrough _render hook_ templates receive the following [context](g): `Attributes` : (`map`) The [Markdown attributes][], available if you configure your site as follows: {{< code-toggle file=hugo >}} [markup.goldmark.parser.attribute] block = true {{< /code-toggle >}} Hugo populates the `Attributes` map for _block_ passthrough elements. Markdown attributes are not applicable to _inline_ elements. `Inner` : (`string`) The inner content of the passthrough element, excluding the delimiters. `Ordinal` : (`int`) The zero-based ordinal of the passthrough element on the page. `Page` : (`page`) A reference to the current page. `PageInner` : (`page`) A reference to a page nested via the [`RenderShortcodes`][] method. [See details](#pageinner-details). `Position` : (`string`) The position of the passthrough element within the page content. `Type` : (`string`) The passthrough element type, either `block` or `inline`. ## Example Instead of client-side JavaScript rendering of mathematical markup using MathJax or KaTeX, create a passthrough render hook which calls the [`transform.ToMath`][] function. ```go-html-template {file="layouts/_markup/render-passthrough.html" copy=true} {{- $opts := dict "output" "htmlAndMathml" "displayMode" (eq .Type "block") }} {{- with try (transform.ToMath .Inner $opts) }} {{- with .Err }} {{- errorf "Unable to render mathematical markup to HTML using the transform.ToMath function. The KaTeX display engine threw the following error: %s: see %s." . $.Position }} {{- else }} {{- .Value }} {{- $.Page.Store.Set "hasMath" true }} {{- end }} {{- end -}} ``` Then, in your base template, conditionally include the KaTeX CSS within the head element: ```go-html-template {file="layouts/baseof.html" copy=true} {{ $noop := .WordCount }} {{ if .Page.Store.Get "hasMath" }} {{ end }} ``` In the above, note the use of a [noop](g) statement to force content rendering before we check the value of `hasMath` with the `Store.Get` method. Although you can use one template with conditional logic as shown above, you can also create separate templates for each [`Type`](#type) of passthrough element: ```tree layouts/ └── _markup/ ├── render-passthrough-block.html └── render-passthrough-inline.html ``` {{% include "/_common/render-hooks/pageinner.md" %}} [Goldmark]: https://github.com/yuin/goldmark [Markdown attributes]: /content-management/markdown-attributes/ [Passthrough]: /configuration/markup/#passthrough [`RenderShortcodes`]: /methods/page/rendershortcodes/ [`transform.ToMath`]: /functions/transform/tomath/ [mathematical expressions]: /content-management/mathematics/