Pandoc

A YAML metadata block is a valid YAML object, delimited by a line of three hyphens (---) at the top and a line of three hyphens (---) or three dots (...) at the bottom. The initial line --- must not be followed by a blank line. A YAML metadata block may occur anywhere in the document, but if it is not at the beginning, it must be preceded by a blank line.

Note that, because of the way pandoc concatenates input files when several are provided, you may also keep the metadata in a separate YAML file and pass it to pandoc as an argument, along with your Markdown files:

Just be sure that the YAML file begins with --- and ends with --- or .... Alternatively, you can use the --metadata-file option. Using that approach however, you cannot reference content (like footnotes) from the main Markdown input document.

Metadata will be taken from the fields of the YAML object and added to any existing document metadata. Metadata can contain lists and objects (nested arbitrarily), but all string scalars will be interpreted as Markdown. Fields with names ending in an underscore will be ignored by pandoc. (They may be given a role by external processors.) Field names must not be interpretable as YAML numbers or boolean values (so, for example, yes, True, and 15 cannot be used as field names).

A document may contain multiple metadata blocks. If two metadata blocks attempt to set the same field, the value from the second block will be taken.

Each metadata block is handled internally as an independent YAML document. This means, for example, that any YAML anchors defined in a block cannot be referenced in another block.

When pandoc is used with -t markdown to create a Markdown document, a YAML metadata block will be produced only if the -s/--standalone option is used. All of the metadata will appear in a single block at the beginning of the document.

Note that YAML escaping rules must be followed. Thus, for example, if a title contains a colon, it must be quoted, and if it contains a backslash escape, then it must be ensured that it is not treated as a YAML escape sequence. The pipe character (|) can be used to begin an indented block that will be interpreted literally, without need for escaping. This form is necessary when the field contains blank lines or block-level formatting:

The literal block after the | must be indented relative to the line containing the |. If it is not, the YAML will be invalid and pandoc will not interpret it as metadata. For an overview of the complex rules governing YAML, see the Wikipedia entry on YAML syntax.

Template variables will be set automatically from the metadata. Thus, for example, in writing HTML, the variable abstract will be set to the HTML equivalent of the Markdown in the abstract field:

This is the abstract.

It consists of two paragraphs.

Variables can contain arbitrary YAML structures, but the template must match this structure. The author variable in the default templates expects a simple list or string, but can be changed to support more complicated structures. The following combination, for example, would add an affiliation to the author if one is given:

To use the structured authors in the example above, you would need a custom template:

Raw content to include in the document’s header may be specified using header-includes; however, it is important to mark up this content as raw code for a particular output format, using the raw_attribute extension, or it will be interpreted as Markdown. For example:

Note: the yaml_metadata_block extension works with commonmark as well as markdown (and it is enabled by default in gfm and commonmark_x). However, in these formats the following restrictions apply:

The YAML metadata block must occur at the beginning of the document (and there can be only one). If multiple files are given as arguments to pandoc, only the first can be a YAML metadata block.

The leaf nodes of the YAML structure are parsed in isolation from each other and from the rest of the document. So, for example, you can’t use a reference link in these contexts if the link definition is somewhere else in the document.