Ubuntu Manpage: lowdown — simple markdown translator library

name
library
synopsis
description
types
abstract syntax tree
see also
authors

Provided by: liblowdown-dev_1.2.0-1_amd64

NAME

     lowdown — simple markdown translator library

LIBRARY

     library “liblowdown”

SYNOPSIS

     #include <sys/queue.h>
     #include <stdio.h>
     #include <lowdown.h>

     struct lowdown_meta
     struct lowdown_node
     struct lowdown_opts

DESCRIPTION

     This library parses lowdown(5) into various output formats.

     The library consists first of a high-level interface consisting of lowdown_buf(3), lowdown_buf_diff(3),
     lowdown_file(3), and lowdown_file_diff(3).

     The high-level functions interface with low-level functions that perform parsing and formatting.  These
     consist of lowdown_doc_new(3), lowdown_doc_parse(3), and lowdown_doc_free(3) for parsing lowdown(5)
     documents into an abstract syntax tree.

     The front-end functions for freeing, allocation, and rendering are as follows.

     •   HTML5:
         lowdown_html_free(3)
         lowdown_html_new(3)
         lowdown_html_rndr(3)

     •   gemini:
         lowdown_gemini_free(3)
         lowdown_gemini_new(3)
         lowdown_gemini_rndr(3)

     •   LaTeX:
         lowdown_latex_free(3)
         lowdown_latex_new(3)
         lowdown_latex_rndr(3)

     •   OpenDocument:
         lowdown_odt_free(3)
         lowdown_odt_new(3)
         lowdown_odt_rndr(3)

     •   roff:
         lowdown_nroff_free(3)
         lowdown_nroff_new(3)
         lowdown_nroff_rndr(3)

     •   UTF-8 ANSI terminal:
         lowdown_term_free(3)
         lowdown_term_new(3)
         lowdown_term_rndr(3)

     •   debugging:
         lowdown_tree_rndr(3)

     To compile and link, use pkg-config(1):

     % cc `pkg-config --cflags lowdown` -c -o sample.o sample.c
     % cc -o sample sample.o `pkg-config --libs lowdown`

   Pledge Promises
     The lowdown library is built to operate in security-sensitive environments, such as those using pledge(2)
     on OpenBSD.  The only promise required is stdio for lowdown_file_diff(3) and lowdown_file(3): both require
     access to the stream for reading input.

TYPES

All lowdown functions use one or more of the following structures.

The main structure for configuring parsing and output is struct lowdown_opts. It has the following fields:

enum lowdown_type type
The output medium:

LOWDOWN_HTML
HTML5
LOWDOWN_LATEX
LaTeX
LOWDOWN_MAN
roff -man macros
LOWDOWN_FODT
“flat” OpenDocument
LOWDOWN_TERM
ANSI-compatible UTF-8 terminal output
LOWDOWN_GEMINI
Gemini format
LOWDOWN_NROFF
roff -ms macros
LOWDOWN_TREE
syntax tree (debugging)

unsigned int feat
Parse-time features. This bit-field may have the following bits OR'd:

LOWDOWN_ATTRS
Parse PHP extra link, header, and image attributes.
LOWDOWN_AUTOLINK
Parse http, https, ftp, mailto, and relative links or link fragments.
LOWDOWN_CALLOUTS
Parse MDN/GFM callouts (“admonitions”).
LOWDOWN_COMMONMARK
Tighten input parsing to the CommonMark specification. This also uses the first ordered
list value instead of starting all lists at one. This feature is experimental and
incomplete.
LOWDOWN_DEFLIST
Parse PHP extra definition lists. This is currently constrained to single-key lists.
LOWDOWN_FENCED
Parse GFM fenced (language-specific) code blocks.
LOWDOWN_FOOTNOTES
Parse MMD style footnotes. This only supports the referenced footnote style, not the
“inline” style.
LOWDOWN_HILITE
Parse highlit sequences. This are disabled by default because it may be erroneously
interpreted as section headers.
LOWDOWN_IMG_EXT
Deprecated. Use LOWDOWN_ATTRS instead.
LOWDOWN_MANTITLE
Recognise manpage titles in Pandoc metadata title lines. Only applicable if
LOWDOWN_METADATA is also provided. Manpages titles must begin with a non-empty title
followed by an open parenthesis, digit or “n”, optional letters after, then a closing
parenthesis. This may be optionally followed by a source and, if a vertical bar is
detected, the content after as the volume. These are passed to the renderers as the title,
volume, and optionally source and volume metadata key-value pairs. The original title is
not recoverable.
LOWDOWN_MATH
Parse mathematics equations.
LOWDOWN_METADATA
Parse in-document metadata.
LOWDOWN_NOCODEIND
Do not parse indented content as code blocks.
LOWDOWN_NOINTEM
Do not parse emphasis within words.
LOWDOWN_STRIKE
Parse strikethrough sequences.
LOWDOWN_SUPER
Parse super-scripts. This accepts foo^bar^ GFM super-scripts.
LOWDOWN_SUPER_SHORT
If LOWDOWN_SUPER is enabled, instead of the GFM style, accept the “short” form of
superscript. This accepts foo^bar, which puts the parts following the caret until
whitespace in superscripts; or foo^(bar), which puts only the parts in parenthesis.
LOWDOWN_TABLES
Parse GFM tables.
LOWDOWN_TASKLIST
Parse GFM task list items.

unsigned int oflags
Output-time features. Bit values are specific to the type and are not guaranteed to be globally
unique.

For all types:

LOWDOWN_SMARTY
Don't use smart typography formatting.
LOWDOWN_STANDALONE
Emit a full document instead of a document fragment. This envelope is largely populated
from metadata if LOWDOWN_METADATA was provided as an option or as given in meta or metaovr.

For LOWDOWN_HTML:

LOWDOWN_HTML_CALLOUT_MDN, LOWDOWN_HTML_CALLOUT_GFM
Output MDN and/or GFM-style callout syntax.
LOWDOWN_HTML_ESCAPE
If LOWDOWN_HTML_SKIP_HTML has not been set, escapes in-document HTML so that it is rendered
as opaque text.
LOWDOWN_HTML_HARD_WRAP
Retain line-breaks within paragraphs.
LOWDOWN_HTML_HEAD_IDS
Have an identifier written with each header element consisting of an HTML-escaped version
of the header contents.
LOWDOWN_HTML_NUM_ENT
Convert, when possible, HTML entities to their numeric form. If not set, the entities are
used as given in the input.
LOWDOWN_HTML_OWASP
When escaping text, be extra paranoid in following the OWASP suggestions for which
characters to escape.
LOWDOWN_HTML_SKIP_HTML
Do not render in-document HTML at all.
LOWDOWN_HTML_TITLEBLOCK
Output a Pandoc-style title block. This is a <header id="title-block-header"> element
right after the opening <body> containing elements for specified title, author(s), and
date. These are <h1> and <p> elements, respectively, with classes set to what's being
output (title, etc.). At least one of these must be specified for the title block to be
output.

For LOWDOWN_GEMINI, there are several flags for controlling link placement. By default, links
(images, autolinks, and links) are queued when specified in-line then emitted in a block sequence
after the nearest block node. (See ABSTRACT SYNTAX TREE.)

LOWDOWN_GEMINI_LINK_END
Emit the queue of links at the end of the document instead of after the nearest block node.
LOWDOWN_GEMINI_LINK_IN
Render all links within the flow of text. This will cause breakage when nested links, such
as images within links, links in blockquotes, etc. It should not be used unless in
carefully crafted documents.
LOWDOWN_GEMINI_LINK_NOREF
Do not format link labels. Takes precedence over LOWDOWN_GEMINI_LINK_ROMAN.
LOWDOWN_GEMINI_LINK_ROMAN
When formatting link labels, use lower-case Roman numerals instead of the default lowercase
hexavigesimal (i.e., “a”, “b”, ..., “aa”, “ab”, ...).
LOWDOWN_GEMINI_METADATA
Print metadata as the canonicalised key followed by a colon then the value, each on one
line (newlines replaced by spaces). The metadata block is terminated by a double newline.
If there is no metadata, this does nothing.

There may only be one of LOWDOWN_GEMINI_LINK_END or LOWDOWN_GEMINI_LINK_IN. If both are specified,
the latter is unset.

For LOWDOWN_FODT:

LOWDOWN_ODT_SKIP_HTML
Do not render in-document HTML at all. Text within HTML elements remains.

For LOWDOWN_LATEX:

LOWDOWN_LATEX_NUMBERED
Use the default numbering scheme for sections, subsections, etc. If not specified, these
are inhibited.
LOWDOWN_LATEX_SKIP_HTML
Do not render in-document HTML at all. Text within HTML elements remains.

For LOWDOWN_MAN and LOWDOWN_NROFF:

LOWDOWN_NROFF_GROFF
Use GNU extensions (i.e., for groff(1)) when rendering output. The groff arguments must
include -mpdfmark for formatting links with LOWDOWN_MAN or -mspdf instead of -ms for
LOWDOWN_NROFF. Applies to the LOWDOWN_MAN and LOWDOWN_NROFF output types.
LOWDOWN_NROFF_NOLINK
Don't show links at all if they have embedded text. Applies to images and regular links.
Only in LOWDOWN_MAN or when LOWDOWN_NROFF_GROFF is not specified.
LOWDOWN_NROFF_NUMBERED
Use numbered sections if LOWDOWON_NROFF_GROFF is not specified. Only applies to the
LOWDOWN_NROFF output type.
LOWDOWN_NROFF_SHORTLINK
Render link URLs in short form. Applies to images, autolinks, and regular links. Only in
LOWDOWN_MAN or when LOWDOWN_NROFF_GROFF is not specified.
LOWDOWN_NROFF_SKIP_HTML
Do not render in-document HTML at all. Text within HTML elements remains.

For LOWDOWN_TERM:

LOWDOWN_TERM_ALL_META
If LOWDOWN_STANDALONE is specified, output all metadata instead of just the title, author,
and date.
LOWDOWN_TERM_NOANSI
Don't apply ANSI style codes at all. This implies LOWDOWN_TERM_NOCOLOUR.
LOWDOWN_TERM_NOCOLOUR
Don't apply ANSI colour codes. This will still show underline, bold, etc. This should not
be used in difference mode, as the output will make no sense.
LOWDOWN_TERM_NOLINK
Don't show links at all. Applies to images and regular links: autolinks are still shown.
This may be combined with LOWDOWN_TERM_SHORTLINK to also shorten autolinks.
LOWDOWN_TERM_SHORTLINK
Render link URLs in short form. Applies to images, autolinks, and regular links. This may
be combined with LOWDOWN_TERM_NOLINK to only show shortened autolinks.

size_t maxdepth
The maximum parse depth before the parser exits. Most documents will have a parse depth in the
single digits.

size_t cols
For LOWDOWN_TERM, the “soft limit” for width of terminal output not including margins. If zero, 80
shall be used.

size_t hmargin
For LOWDOWN_TERM, the left margin (space characters).

size_t vmargin
For LOWDOWN_TERM, the top/bottom margin (newlines).

struct lowdown_opts_nroff nroff
If type is LOWDOWN_MAN or LOWDOWN_NROFF, this contains constant-width font variants: const char *cr
for roman constant-width, const char *cb for bold, const char *ci for italic, and const char *cbi
for bold-italic. If any of these are NULL, they default to their constant-width variants.

struct lowdown_opts_odt odt
If type is LOWDOWN_FODT, this contains const char *sty, which is either NULL or the OpenDocument
styles used when creating standalone documents. If NULL, the default styles are used.

char **meta
An array of metadata key-value pairs or NULL. Each pair must appear as if provided on one line (or
multiple lines) of the input, including the terminating newline character. If not consisting of a
valid pair (e.g., no newline, no colon), then it is ignored. When processed, these values are
overridden by those in the document (if LOWDOWN_METADATA is specified) or by those in metaovr.

size_t metasz
Number of pairs in metaovr.

char **metaovr
See meta. The difference is that metaovr is applied after meta and in-document metadata, so it
overrides prior values.

size_t metaovrsz
Number of pairs in metaovr.

Parsed metadata is held in key-value struct lowdown_meta pairs, or collectively as struct lowdown_metaq, if
LOWDOWN_METADATA is set in feat. The former structure consists of the following fields:

char *key
The metadata key in its canonical form: lowercase alphanumerics, hyphen, and underscore.
Whitespace is removed and other characters replaced by a question mark.

char *value
The metadata value. This may be an empty string.

The abstract syntax tree is encoded in struct lowdown_node, which consists of the following.

enum lowdown_rndrt type
The node type, using HTML5 output as an illustration:

LOWDOWN_BLOCKCODE
A block-level snippet of code described by <pre><code>.
LOWDOWN_BLOCKHTML
A block-level snippet of HTML. This is simply opaque HTML content.
LOWDOWN_BLOCKQUOTE
A block-level quotation described by <blockquote>.
LOWDOWN_CODESPAN
An inline-level snippet of code described by <code>.
LOWDOWN_DEFINITION
A definition list described by <dl>.
LOWDOWN_DEFINITION_DATA
Definition data described by <dd>.
LOWDOWN_DEFINITION_TITLE
Definition title described by <dt>.
LOWDOWN_DOC_HEADER
Container for metadata described by <head>.
LOWDOWN_DOUBLE_EMPHASIS
Bold (or otherwise notable) content described by <strong>.
LOWDOWN_EMPHASIS
Italic (or otherwise notable) content described by <em>.
LOWDOWN_ENTITY
Named or numeric HTML entity.
LOWDOWN_FOOTNOTE
Footnote content.
LOWDOWN_HEADER
A block-level header described by one of <h1> through <h6>.
LOWDOWN_HIGHLIGHT
Marked test described by <mark>.
LOWDOWN_HRULE
A horizontal line described by <hr>.
LOWDOWN_IMAGE
An image described by <img>.
LOWDOWN_LINEBREAK
A hard line-break within a block context described by <br>.
LOWDOWN_LINK
A link to external media described by <a>. Links may contain limited child markup, but not
nested links.
LOWDOWN_LINK_AUTO
Like LOWDOWN_LINK, except inferred from text content.
LOWDOWN_LIST
A list enclosure described by <ul> or <ol>.
LOWDOWN_LISTITEM
A list item described by <li>.
LOWDOWN_MATH_BLOCK
A snippet of mathematical text in LaTeX format described within \[xx\] or \(xx\). This is
usually (in HTML) externally handled by a JavaScript renderer.
LOWDOWN_META
Meta-data keys and values. These are described by elements in <head>.
LOWDOWN_NORMAL_TEXT
Normal text content.
LOWDOWN_PARAGRAPH
A block-level paragraph described by <p>.
LOWDOWN_RAW_HTML
An inline of raw HTML. (Only if configured during parse.)
LOWDOWN_ROOT
The root of the document. This is always the topmost node, and the only node where the
parent field is NULL.
LOWDOWN_STRIKETHROUGH
Content struck through. Described by <del>.
LOWDOWN_SUBSCRIPT, LOWDOWN_SUPERSCRIPT
A subscript or superscript described by <sub> or <sup>, respectively.
LOWDOWN_TABLE_BLOCK
A table block described by <table>.
LOWDOWN_TABLE_BODY
A table body section described by <tbody>.
LOWDOWN_TABLE_CELL
A table cell described by <td>, or <th> if in the header.
LOWDOWN_TABLE_HEADER
A table header section described by <thead>.
LOWDOWN_TABLE_ROW
A table row described by <tr>.
LOWDOWN_TRIPLE_EMPHASIS
Combination of LOWDOWN_EMPHASIS and LOWDOWN_DOUBLE_EMPHASIS.

size_t id
An identifier unique within the document. This can be used as a table index since the number is
assigned from a monotonically increasing point during the parse.

struct lowdown_node *parent
The parent of the node, or NULL at the root.

enum lowdown_chng chng
Change tracking: whether this node was inserted (LOWDOWN_CHNG_INSERT), deleted
(LOWDOWN_CHNG_DELETE), or neither (LOWDOWN_CHNG_NONE).

struct lowdown_nodeq children
A possibly-empty list of child nodes.

<anon union>
An anonymous union of type-specific structures.

rndr_autolink
For LOWDOWN_LINK_AUTO, the link address as link and the link type type, which may be one of
HALINK_EMAIL for e-mail links and HALINK_NORMAL otherwise. Any buffer may be empty-sized.
rndr_blockcode
For LOWDOWN_BLOCKCODE, the opaque text of the block and the optional lang of the code
language.
rndr_blockhtml
For LOWDOWN_BLOCKHTML, the opaque HTML text.
rndr_codespan
The opaque text of the contents.
rndr_definition
For LOWDOWN_DEFINITION, containing flags that may be HLIST_FL_BLOCK if the definition list
should be interpreted as containing block nodes.
rndr_entity
For LOWDOWN_ENTITY, the entity text.
rndr_header
For LOWDOWN_HEADER, the level of the header starting at zero (this value is relative to the
metadata base header level, defaulting to one), optional space-separated class list
attr_cls, and optional single identifier attr_id.
rndr_image
For LOWDOWN_IMAGE, the image address link, the image title title, dimensions NxN (width by
height) in dims, and alternate text alt. CSS in-line style for width and height may be
given in attr_width and/or attr_height, and a space-separated list of classes may be in
attr_cls and a single identifier may be in attr_id.
rndr_link
Like rndr_autolink, but without a type and further defining an optional link title title,
optional space-separated class list attr_cls, and optional single identifier attr_id.
rndr_list
For LOWDOWN_LIST, consists of a bitfield flags that may be set to HLIST_FL_ORDERED for an
ordered list and HLIST_FL_UNORDERED for an unordered one. If HLIST_FL_BLOCK is set, the
list should be output as if items were separate blocks. The start value for
HLIST_FL_ORDERED is the starting list item position, which is one by default and never
zero. The items is the number of list items.
rndr_listitem
For LOWDOWN_LISTITEM, consists of a bitfield flags that may be set to HLIST_FL_ORDERED for
an ordered list, HLIST_FL_UNORDERED for an unordered list, HLIST_FL_DEF for definition list
data, HLIST_FL_CHECKED or HLIST_FL_UNCHECKED for an unordered “task” list, and/or
HLIST_FL_BLOCK for list item output as if containing block nodes. The HLIST_FL_BLOCK
should not be used: use the parent list (or definition list) flags for this. The num is
the index in a HLIST_FL_ORDERED list. It is monotonically increasing with each item in the
list, starting at the start variable given in struct rndr_list.
rndr_math
For LOWDOWN_MATH, the mode of display in blockmode: if 1, in-line math; if 2, multi-line.
The opaque equation, which is assumed to be in LaTeX format, is in the opaque text.
rndr_meta
Each LOWDOWN_META key-value pair is represented. The keys are lower-case without spaces or
non-ASCII characters. If provided, enclosed nodes may consist only of LOWDOWN_NORMAL_TEXT
and LOWDOWN_ENTITY.
rndr_normal_text
The basic text content for LOWDOWN_NORMAL_TEXT. If flags is set to HTEXT_ESCAPED, the text
may be escaped for output, but may not be altered by any smart typography or similar (it
should be passed as-is).
rndr_paragraph
For LOWDOWN_PARAGRAPH, species how many lines the paragraph has in the input file and
beoln, set to non-zero if the paragraph ends with an empty line instead of a breaking block
node.
rndr_raw_html
For LOWDOWN_RAW_HTML, the opaque HTML text.
rndr_table
For LOWDOWN_TABLE_BLOCK, the number of columns in each row or header row. The number of
columns in rndr_table, rndr_table_header, and rndr_table_cell are the same.
rndr_table_cell
For LOWDOWN_TABLE_CELL, the current col column number out of columns. See
rndr_table_header for a description of the bits in flags. The number of columns in
rndr_table, rndr_table_header, and rndr_table_cell are the same.
rndr_table_header
For LOWDOWN_TABLE_HEADER, the number of columns in each row and the per-column flags, which
may tested for equality against HTBL_FL_ALIGN_LEFT, HTBL_FL_ALIGN_RIGHT, or
HTBL_FL_ALIGN_CENTER after being masked with HTBL_FL_ALIGNMASK; or HTBL_FL_HEADER. If no
alignment is specified after the mask, the default should be left-aligned. The number of
columns in rndr_table, rndr_table_header, and rndr_table_cell are the same.

ABSTRACT SYNTAX TREE

     A parsed document is a tree of struct lowdown_node nodes.  If a node is “block”, it may contain other block
     or inline nodes.  If “inline,” it may only contain other inline nodes.  “Special” nodes are documented
     below.  An additional mark of “void” means that the node will never contain children.

           Node                        Scope
           LOWDOWN_BLOCKCODE           block, void
           LOWDOWN_BLOCKHTML           block, void
           LOWDOWN_BLOCKQUOTE          block
           LOWDOWN_CODESPAN            inline, void
           LOWDOWN_DEFINITION          block
           LOWDOWN_DEFINITION_DATA     special
           LOWDOWN_DEFINITION_TITLE    special
           LOWDOWN_DOC_HEADER          special
           LOWDOWN_DOUBLE_EMPHASIS     inline
           LOWDOWN_EMPHASIS            inline
           LOWDOWN_ENTITY              inline, void
           LOWDOWN_FOOTNOTE            block, special
           LOWDOWN_HEADER              block
           LOWDOWN_HRULE               inline, void
           LOWDOWN_IMAGE               inline, void
           LOWDOWN_LINEBREAK           inline, void
           LOWDOWN_LINK                inline
           LOWDOWN_LINK_AUTO           inline, void
           LOWDOWN_LIST                block
           LOWDOWN_LISTITEM            special
           LOWDOWN_MATH_BLOCK          inline, void
           LOWDOWN_META                special
           LOWDOWN_NORMAL_TEXT         inline, void
           LOWDOWN_PARAGRAPH           block
           LOWDOWN_RAW_HTML            inline, void
           LOWDOWN_ROOT                special
           LOWDOWN_STRIKETHROUGH       inline
           LOWDOWN_SUBSCRIPT           inline
           LOWDOWN_SUPERSCRIPT         inline
           LOWDOWN_TABLE_BLOCK         block
           LOWDOWN_TABLE_BODY          special
           LOWDOWN_TABLE_CELL          special
           LOWDOWN_TABLE_HEADER        special
           LOWDOWN_TABLE_ROW           special
           LOWDOWN_TRIPLE_EMPHASIS     inline

     The general structure of the AST is as follows.  Nodes have no order imposed on them unless as noted:

     -   LOWDOWN_ROOT (ordered)
         -   LOWDOWN_DOC_HEADER
             -   LOWDOWN_META
                 -   LOWDOWN_ENTITY
                 -   LOWDOWN_NORMAL_TEXT
         -   (zero or more block nodes)

     Special nodes have specific placement within their parents as follows:

     -   LOWDOWN_DEFINITION (one or more ordered pairs of...)
         -   LOWDOWN_DEFINITION_TITLE
             -   (inline nodes)
         -   LOWDOWN_DEFINITION_DATA
             -   (block nodes)

     -   LOWDOWN_HEADER
         -   (inline nodes)

     -   LOWDOWN_LIST
         -   LOWDOWN_LISTITEM
             -   (inline or block nodes, depending)

     -   LOWDOWN_TABLE_BLOCK (ordered)
         -   LOWDOWN_TABLE_HEADER (zero or more...)
             -   LOWDOWN_TABLE_ROW (one or more...)
                 -   LOWDOWN_TABLE_CELL
                     -   (inline nodes)
         -   LOWDOWN_TABLE_BODY (zero or more...)
             -   LOWDOWN_TABLE_ROW (one or more...)
                 -   LOWDOWN_TABLE_CELL
                     -   (inline nodes)

     Lastly, LOWDOWN_FOOTNOTE may appear anywhere in the document and contains block nodes.

AUTHORS

     lowdown was forked from hoedown: https://github.com/hoedown/hoedown by Kristaps Dzonsons, kristaps@bsd.lv.
     It has been considerably modified since.