Pandoc::Elements - create and process Pandoc documents


    The output of this script

        use Pandoc::Elements;
        use JSON;
        print Document(
                title => MetaInlines [ Str "Greeting" ]
                Header( 1, attributes { id => 'top' }, [ Str 'Hello' ] ),
                Para [ Str 'Hello, world!' ],
            api_version => ''

    can be converted for instance to HTML via

        ./ | pandoc -f json -t html5 --standalone

    an equivalent Pandoc Markdown document would be

        % Greeting
        # Gruß {.de}
        Hello, world!


    Pandoc::Elements provides utility functions to parse, serialize, and
    modify abstract syntax trees (AST) of Pandoc <>
    documents. Pandoc can convert this data structure to many other
    document formats, such as HTML, LaTeX, ODT, and ePUB.

    See also module Pandoc::Filter, command line script pod2pandoc, and the
    internal modules Pandoc::Walker and Pod::Simple::Pandoc.


    The Pandoc document model is defined in file Text.Pandoc.Definition
    as part of Haskell package pandoc-types.

    Pandoc::Elements is compatible with pandoc-types 1.12.3 (released with
    pandoc 1.12.1) up to at least pandoc-types- (first releases
    with pandoc 1.18). JSON output of all pandoc releases since 1.12.1 can
    be parsed with function pandoc_json, the "Document" constructor or
    method parse of module Pandoc. The AST is always upgraded to
    pandoc-types 1.17 and downgraded to another api version on
    serialization with to_json.

    To determine the api version required by a version of pandoc executable
    since version 1.18 execute pandoc with the --version option and check
    which version of the pandoc-types library pandoc was compiled with.

    Beginning with version 1.18 pandoc will not decode a JSON AST
    representation unless the major and minor version numbers (Document
    method api_version) match those built into that version of pandoc. The
    following changes in pandoc document model have been implemented:

      * pandoc-types 1.17, released for pandoc 1.18, introduced the
      LineBlock element and modified representation of the root Document

      * pandoc-types 1.16, released with pandoc 1.16, introduced attributes
      to Link and Image elements

      * pandoc-types 1.12.3, released with pandoc 1.12.1, modified the
      representation of elements to objects with field t and c. This is
      also the internal representation of documents used in this module.


    The following functions and keywords are exported by default:

      * Constructors for all Pandoc document element (block elements such
      as Para and inline elements such as Emph, metadata elements and the

      * Type keywords such as Decimal and LowerAlpha to be used as types in
      other document elements.

      * The following helper functions pandoc_json, pandoc_version,
      attributes, metadata, citation, and element.

 pandoc_json $json

    Parse a JSON string, as emitted by pandoc in JSON format. This is the
    reverse to method to_json but it can read both old (before Pandoc 1.16)
    and new format.

 attributes { key => $value, ... }

    Maps a hash reference or instance of Hash::MultiValue into the internal
    structure of Pandoc attributes. The special keys id (string), and class
    (string or array reference with space-separated class names) are
    recognized. See attribute methods for details.

 citation { ... }

    A citation as part of document element Cite must be a hash reference
    with fields citationId (string), citationPrefix (list of inline
    elements) citationSuffix (list of inline elements), citationMode (one
    of NormalCitation, AuthorInText, SuppressAuthor), citationNoteNum
    (integer), and citationHash (integer). The helper method citation can
    be used to construct such a hash by filling in default values and
    optionally using shorter field names (id, prefix, suffix, mode, note,
    and hash):

        citation {
            id => 'foo',
            prefix => [ Str "see" ],
            suffix => [ Str "p.", Space, Str "42" ]
        # in Pandoc Markdown
        [see @foo p. 42]

    The values returned by this function, as well as any citations
    contained in document objects returned by pandoc_json, are blessed
    hashrefs with getter/setter accessors corresponding to both the full
    and short field names, so that e.g. $citation->citationId(...) and
    $citation->id(...) get or set the same value.

 pandoc_version( [ $document ] )

    Return a Pandoc::Version object with expected version number of pandoc
    executable to be used for serializing documents with to_json.

    If a Document element is given as argument, the minimal pandoc release
    version compatible with its api version is returned.

    Without argument, package variable $PANDOC_VERSION is checked for a
    preferred pandoc release. By default this variable is set from an
    environment variable of same name. If no preferred pandoc release has
    been specified, the function returns version 1.18 because this is the
    first pandoc release compatible with most recent api version supported
    by this module.

    See also method version of module Pandoc to get the current version of
    pandoc executable on your system.

 element( $name => $content )

    Create a Pandoc document element of arbitrary name. This function is
    only exported on request.


    Document elements are encoded as Perl data structures equivalent to the
    JSON structure, emitted with pandoc output format json. This JSON
    structure is subject to minor changes between versions of pandoc. All
    elements are blessed objects that provide common element methods (all
    elements), attribute methods (elements with attributes), and additional
    element-specific methods.



    Return the element as JSON encoded string. The following are


    The serialization format can be adjusted to different pandoc versions
    with module and environment variable PANDOC_VERSION or with Document
    element properties api_version and pandoc_version.

    When writing filters you can normally just rely on the api version
    value obtained from pandoc, since pandoc expects to receive the same
    JSON format as it emits.


    Return the name of the element, e.g. "Para" for a paragraph element.


    Return the element content. For most elements (Para, Emph, Str...) the
    content is an array reference with child elements. Other elements
    consist of multiple parts; for instance the Link element has attributes
    (attr, id, class, classes, keyvals) a link text (content) and a link
    target (target) with url and title.


    True if the element is a Block element


    True if the element is an inline Inline element


    True if the element is a Metadata element


    True if the element is a Document element


    Return the element unmodified if it is a block element or wrapped in a
    Plain or Div otherwise.

  match( $selector )

    Check whether the element matches a given Pandoc::Selector (given as
    instance or string).


    Walk the element tree with Pandoc::Walker


    Query the element to extract results with Pandoc::Walker


    Transform the element tree with Pandoc::Walker


    Returns a concatenated string of element content, leaving out all


    Some elements have attributes which can be an identifier, ordered class
    names and ordered key-value pairs. Elements with attributes provide the
    following methods:


    Get or set the attributes in Pandoc internal structure:

      [ $id, [ @classes ], [ [ key => $value ], ... ] ]

    See helper function attributes to create this structure.


    Get all attributes (id, class, and key-value pairs) as new
    Hash::MultiValue instance, or replace all key-value pairs plus id
    and/or class if these are included as field names. All class fields are
    split by whitespaces.

      $e->keyvals                           # return new Hash::MultiValue
      $e->keyvals( $HashMultiValue )        # update by instance of Hash::MultiValue
      $e->keyvals( key => $value, ... )     # update by list of key-value pairs
      $e->keyvals( \%hash )                 # update by hash reference
      $e->keyvals( { } )                    # remove all key-value pairs
      $e->keyvals( id => '', class => '' )  # remove all key-value pairs, id, class


    Get or set the identifier. See also Pandoc::Filter::HeaderIdentifiers
    for utility functions to handle Header identifiers.


    Get or set the list of classes, separated by whitespace.

  add_attribute( $name => $value )

    Append an attribute. The special attribute names id and class set or
    append identifier or class, respectively.



    Root element, consisting of metadata hash (meta), document element
    array (content=blocks) and optional api_version. The constructor
    accepts either two arguments and an optional named parameter

        Document { %meta }, [ @blocks ], api_version => $version_string

    or a hash with three fields for metadata, document content, and an
    optional pandoc API version:

            meta               => { %metadata },
            blocks             => [ @content ],
            pandoc-api-version => [ $major, $minor, $revision ]

    The latter form is used as pandoc JSON format since pandoc release
    1.18. If no api version is given, it will be set 1.17 which was also
    introduced with pandoc release 1.18.

    A third ("old") form is accepted for compatibility with pandoc JSON
    format before release 1.18 and since release 1.12.1: an array with two
    elements for metadata and document content respectively.

        [ { unMeta => { %meta } }, [ @blocks ] ]

    The api version is set to 1.16 in this case, but older versions down to
    1.12.3 used the same format.

    Document elements provide the following special methods in addition to
    common element methods:

    api_version( [ $api_version ] )

      Return the pandoc-types version (aka "pandoc-api-version") of this
      document as Pandoc::Version object or sets it to a new value. This
      version determines how method to_json serializes the document.

      See "PANDOC VERSIONS" for details.

    pandoc_version( [ $pandoc_version ] )

      Return the minimum required version of pandoc executable compatible
      with the api_version of this document. The following are equivalent:

        pandoc_version( $doc );

      If used as setter, sets the api version of this document to be
      compatible with the given pandoc version.

    content or blocks

      Get or set the array of block elements of the document.

    meta( [ $metadata ] )

      Get and/or set combined document metadata. Use method value to get
      selected metadata fields and values.

    value( [ $pointer ] [ %options ] )

      Get selected document metadata field value(s). See Pandoc::Metadata
      for documentation. Can also be called as metavalue, so the following
      are equivalent:

        $doc->value( ... );
        $doc->meta->value( ... );
        $doc->metavalue( ... );

    to_pandoc( [ [ $pandoc, ] @arguments ])

      Process the document with Pandoc executable and return its output:

          $doc->to_pandoc( -o => 'doc.html' );
          my $markdown = $doc->to_pandoc( -t => 'markdown' );

      The first argument can optionally be an instance of Pandoc to use a
      specific executable.

    to_...( [ @arguments ] )

      Process the document into markdown (pandoc's extended Markdown),
      latex (LaTeX), html (HTML), rst (reStructuredText), or plain (plain
      text). The following are equivalent:

          $doc->to_markdown( @args );
          $doc->to_pandoc( @args, '-t' => 'markdown' );

    outline( [ $depth ] )

      Returns an outline of the document structure based on Header
      elements. The outline is a hierarchical hash reference with the
      following fields:


	Header element (not included at the document root)


	List of block elements before the next Header element (of given
	depth or less if a maximum depth was given)


	List of subsections, each having the same outline structure.



    Block quote, consisting of a list of blocks (content)

        BlockQuote [ @blocks ]


    Unnumbered list of items (content=items), each a list of blocks

        BulletList [ [ @blocks ] ]


    Code block (literal string content) with attributes (attr, id, class,
    classes, keyvals)

        CodeBlock $attributes, $content


    Definition list, consisting of a list of pairs (content=items), each a
    term (term, a list of inlines) and one or more definitions
    (definitions, a list of blocks).

        DefinitionList [ @definitions ]
        # each item in @definitions being a pair of the form
            [ [ @inlines ], [ @blocks ] ]


    Generic container of blocks (content) with attributes (attr, id, class,
    classes, keyvals).

        Div $attributes, [ @blocks ]


    Header with level (integer), attributes (attr, id, class, classes,
    keyvals), and text (content, a list of inlines).

        Header $level, $attributes, [ @inlines ]


    Horizontal rule



    List of lines (content), each a list of inlines.

        LineBlock [ @lines ]

    This element was added in pandoc 1.18. Before it was represented Para
    elements with embedded LineBreak elements. This old serialization form
    can be enabled by setting $PANDOC_VERSION package variable to a lower
    version number.





    Numbered list of items (content=items), each a list of blocks),
    preceded by list attributes (start number, numbering style, and

        OrderedList [ $start, $style, $delim ], [ [ @blocks ] ]

    Supported styles are DefaultStyle, Example, Decimal, LowerRoman,
    UpperRoman, LowerAlpha, and UpperAlpha.

    Supported delimiters are DefaultDelim, Period, OneParen, and TwoParens.


    Paragraph, consisting of a list of Inline elements (content).

        Para [ $elements ]


    Plain text, not a paragraph, consisting of a list of Inline elements

        Plain [ @inlines ]


    Raw block with format and content string.

        RawBlock $format, $content


    Table, with caption, column alignments, relative column widths (0 =
    default), column headers (each a list of blocks), and rows (each a list
    of lists of blocks).

        Table [ @inlines ], [ @alignments ], [ @width ], [ @headers ], [ @rows ]

    Possible alignments are AlignLeft, AlignRight, AlignCenter, and

    An example:

        Table [Str "Example"], [AlignLeft,AlignRight], [0.0,0.0],
         [[Plain [Str "name"]]
         ,[Plain [Str "number"]]],
         [[[Plain [Str "Alice"]]
          ,[Plain [Str "42"]]]
         ,[[Plain [Str "Bob"]]
          ,[Plain [Str "23"]]]];



    Citation, a list of citations and a list of inlines (content). See
    helper function citation to construct citations.

        Cite [ @citations ], [ @inlines ]


    Inline code, a literal string (content) with attributes (attr, id,
    class, classes, keyvals)

        Code attributes { %attr }, $content


    Emphasized text, a list of inlines (content).

        Emph [ @inlines ]


    Image with alt text (content, a list of inlines) and target (list of
    url and title) with attributes (attr, id, class, classes, keyvals).

        Image attributes { %attr }, [ @inlines ], [ $url, $title ]

    Serializing the attributes is disabled in api version less then 1.16.


    Hard line break



    Hyperlink with link text (content, a list of inlines) and target (list
    of url and title) with attributes (attr, id, class, classes, keyvals).

        Link attributes { %attr }, [ @inlines ], [ $url, $title ]

    Serializing the attributes is disabled in api version less then 1.16.


    TeX math, given as literal string (content) with type (one of
    DisplayMath and InlineMath).

        Math $type, $content


    Footnote or Endnote, a list of blocks (content).

        Note [ @blocks ]


    Quoted text with quote type (one of SingleQuote and DoubleQuote) and a
    list of inlines (content).

        Quoted $type, [ @inlines ]


    Raw inline with format (a string) and content (a string).

        RawInline $format, $content


    Small caps text, a list of inlines (content).

        SmallCaps [ @inlines ]


    Soft line break


    This element was added in pandoc 1.16 as a matter of editing
    convenience to preserve line breaks (as opposed to paragraph breaks)
    from input source to output. If you are going to feed a document
    containing SoftBreak elements to Pandoc < 1.16 you will have to set the
    package variable or environment variable PANDOC_VERSION to 1.15 or


    Inter-word space



    Generic container of inlines (content) with attributes (attr, id,
    class, classes, keyvals).

        Span attributes { %attr }, [ @inlines ]


    Plain text, a string (content).

        Str $content


    Strikeout text, a list of inlines (content).

        Strikeout [ @inlines ]


    Strongly emphasized text, a list of inlines (content).

        Strong [ @inlines ]


    Subscripted text, a list of inlines (content).

        Supscript [ @inlines ]


    Superscripted text, a list of inlines (content).

        Superscript [ @inlines ]


    See Pandoc::Metadata for documentation of metadata elements MetaBool,
    MetaString, MetaMap, MetaInlines, MetaList, and MetaBlocks.

    Helper function metadata can be used to convert scalars, hash
    references, array references, and Pandoc Inline/Block elements into
    metadata elements.


    The following document elements are only as used as type keywords in
    other document elements:

      * SingleQuote, DoubleQuote

      * DisplayMath, InlineMath

      * AuthorInText, SuppressAuthor, NormalCitation

      * AlignLeft, AlignRight, AlignCenter, AlignDefault

      * DefaultStyle, Example, Decimal, LowerRoman, UpperRoman, LowerAlpha,

      * DefaultDelim, Period, OneParen, TwoParens


    Perl module Pandoc implements a wrapper around the pandoc executable.

    Similar libraries in other programming languages are listed at


    Jakob Voß <>


    Benct Philip Jonsson <>

    TakeAsk <>


    Copyright 2014- Jakob Voß

    GNU General Public License, Version 2

    This module is heavily based on Pandoc by John MacFarlane.