Expressions

Use {{ expression }} in Markdown body text to interpolate values. Statements are not allowed — only expressions.

Variable reference

Hello {{ name }}!

Member access and computed keys work like JavaScript:

{{ user.name }}
{{ items[index] }}

Default values (pipe)

Use | for fallback when the left side is falsy (undefined, null, "", 0, false):

{{ title | "Untitled" }}
{{ count | 0 }}

Ternary operator

{{ isNight ? "Dark" : "Light" }}

Triple braces

{{{ expression }}} is supported. Currently behaves the same as {{ }} (no escaping). Reserved for a future escaping mode.

Component calls

Registered components are called inside expressions:

{{ cityItem({ city: "Osaka", population: 2825000 }) }}

See Includes and components.

Fence `${}` interpolation

Inside fenced code blocks (``` / ~~~), ${expr} expands like a JavaScript template literal:

```markdown
# ${title}
```

Rules:

Same allowed expressions as ${} inside @hg backtick strings (.toLocaleString / .length OK; no component calls)
Outside fences, ${…} stays literal
Escape with \${
Separate from Mustache {{ }} / {{{ }}} (those still expand inside fences)

What you cannot write

Statements (const, if, loops)
Arbitrary function calls (only registered components)
Most method calls (only .toLocaleString; property .length is allowed)

Logic belongs in @hg blocks. See Hyogen blocks.

Escaping

{{ }} does not HTML-escape output. Sanitize downstream if you render to HTML. Suspicious context values may emit warnings — see Paths and security.