Function parse_frontmatter 

pub fn parse_frontmatter(
    source: &str,
) -> Result<(Frontmatter, &str), TemplateError>

Parse YAML frontmatter delimited by --- lines.

Returns the parsed Frontmatter and a string slice pointing to the template body after the closing ---.

Errors

Returns TemplateError::Syntax if the frontmatter block is missing, unclosed, or contains invalid declarations.