Unstable Rust feature "frontmatter"

[frontmatter]

Frontmatter

[frontmatter.syntax]

^Lexer
FRONTMATTER →
      FRONTMATTER_FENCE HORIZONTAL_WHITESPACE^* INFOSTRING^? HORIZONTAL_WHITESPACE^* LF
      ( FRONTMATTER_LINE LF )^*
      FRONTMATTER_FENCE​¹ HORIZONTAL_WHITESPACE^* LF

Show Railroad

[frontmatter.intro]

Frontmatter is an optional section for content intended for external tools without requiring these tools to have full knowledge of the Rust grammar.

#!/usr/bin/env cargo
---
[dependencies]
fastrand = "2"
---

fn main() {
    let num = fastrand::i32(..);
    println!("{num}");
}

[frontmatter.document]

Frontmatter may only be preceded by a shebang and whitespace.

[frontmatter.fence]

The delimiters are referred to as a fence. The opening and closing fences must be at the start of a line. They must be a matching pair of three or more hyphens (-). A fence may be followed by horizontal whitespace.

[frontmatter.infostring]

Following the opening fence may be an infostring for identifying the intention of the contained content. An infostring may be followed by horizontal whitespace.

[frontmatter.body]

The body of the frontmatter may contain any content except for a line starting with as many or more hyphens (-) than in the fences.