Ubuntu Manpage: lowdown — simple markdown translator library

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Provided by: liblowdown-dev_0.10.0-1_amd64

NAME

     lowdown — simple markdown translator library

LIBRARY

     library “liblowdown”

SYNOPSIS

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

     struct lowdown_metadata
     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 struct lowdown_opts structure manage features. It has the following fields:

unsigned int feat
Features used during the parse. This bit-field may have the following bits OR'd:

LOWDOWN_ATTRS
Parse PHP extra link and image attributes.
LOWDOWN_AUTOLINK
Parse http, https, ftp, mailto, and relative links or link fragments.
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_MATH
Parse mathematics equations.
LOWDOWN_METADATA
Parse in-document MMD metadata. For the first paragraph to count as meta-data, the
first line must have a colon in it.
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, 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.

The default value is zero (none).

unsigned int oflags
Features used by the output generators. This bit-field may have the following enabled. Note
that bits are by definition specific to an output type.

For LOWDOWN_HTML:

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_OWASP
When escaping text, be extra paranoid in following the OWASP suggestions for which
characters to escape.
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_SKIP_HTML
Do not render in-document HTML at all.

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 element.

LOWDOWN_GEMINI_LINK_END
Emit the queue of links at the end of the document instead of after the nearest block
element.
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.

And 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_NUMBERED
Use numbered sections if LOWDOWON_NROFF_GROFF is not specified. Only applies to the
LOWDOWN_NROFF output type.
LOWDOWN_NROFF_SKIP_HTML
Do not render in-document HTML at all. Text within HTML elements remains.
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_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.

For LOWDOWN_TERM:

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.

For any mode, you may specify:

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.

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).

enum lowdown_type type
May be set to LOWDOWN_HTML for HTML5 output, LOWDOWN_LATEX for LaTeX, LOWDOWN_MAN for -man
macros, LOWDOWN_FODT for “flat” OpenDocument, LOWDOWN_TERM for ANSI-compatible UTF-8 terminal
output, LOWDOWN_GEMINI for the Gemini format, or LOWDOWN_NROFF for -ms macros. The
LOWDOWN_TREE type causes a debug tree to be written.

Both LOWDOWN_MAN and LOWDOWN_NROFF will use troff tables, which usually require the tbl(1)
preprocessor.

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.

Another common structure is struct lowdown_metadata, which is used to hold parsed (and output-formatted)
metadata keys and values if LOWDOWN_METADATA was provided as an input bit. This structure consists of the
following fields:

char *key
The metadata key in its lowercase, canonical form.

char *value
The metadata value as rendered in the current output format. 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. (Described below.)

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. See below for a description of each one.

The nodes may be one of the following types, with default rendering in HTML5 to illustrate functionality.

LOWDOWN_BLOCKCODE
A block-level (and possibly language-specific) snippet of code. Described by the <pre><code>
elements.

LOWDOWN_BLOCKHTML
A block-level snippet of HTML. This is simply opaque HTML content. (Only if configured
during parse.)

LOWDOWN_BLOCKQUOTE
A block-level quotation. Described by the <blockquote> element.

LOWDOWN_CODESPAN
A snippet of code. Described by the <code> element.

LOWDOWN_DOC_FOOTER
Closes out the document opened in LOWDOWN_DOC_HEADER.

LOWDOWN_DOC_HEADER
A header with data gathered from document metadata (if configured). Described by the <head>
element. (Only if configured during parse.)

LOWDOWN_DOUBLE_EMPHASIS
Bold (or otherwise notable) content. Described by the <strong> element.

LOWDOWN_EMPHASIS
Italic (or otherwise notable) content. Described by the <em> element.

LOWDOWN_ENTITY
An HTML entity, which may either be named or numeric.

LOWDOWN_FOOTNOTE_DEF
A footnote within a LOWDOWN_FOOTNOTES_BLOCK node. Described by the <li id="fnXX"> element.
(Only if configured during parse.)

LOWDOWN_FOOTNOTE_REF
A reference to a LOWDOWN_FOOTNOTE_DEF. Described by the <sup><a> elements. (Only if
configured during parse.)

LOWDOWN_FOOTNOTES_BLOCK
A block of footnotes. Described by the <div class="footnotes"><hr /><ol> elements. (Only if
configured during parse.)

LOWDOWN_HEADER
A block-level header. Described (in the HTML case) by one of <h1> through <h6>.

LOWDOWN_HIGHLIGHT
Marked test. Described by the <mark> element. (Only if configured during parse.)

LOWDOWN_HRULE
A horizontal line. Described by <hr>.

LOWDOWN_IMAGE
An image. Described by the <img> element.

LOWDOWN_LINEBREAK
A hard line-break within a block context. Described by the <br> element.

LOWDOWN_LINK
A link to external media. Described by the <a> element.

LOWDOWN_LINK_AUTO
Like LOWDOWN_LINK, except inferred from text content. Described by the <a> element. (Only
if configured during parse.)

LOWDOWN_LIST
A block-level list enclosure. Described by <ul> or <ol>.

LOWDOWN_LISTITEM
A block-level list item, always appearing within a LOWDOWN_LIST. Described by <li>.

LOWDOWN_MATH_BLOCK
A block (or inline) of mathematical text in LaTeX format. Described within \[xx\] or \(xx\).
This is usually (in HTML) externally handled by a JavaScript renderer. (Only if configured
during parse.)

LOWDOWN_META
Meta-data keys and values. (Only if configured during parse.) These are described by
elements in the <head> element.

LOWDOWN_NORMAL_TEXT
Normal text content.

LOWDOWN_PARAGRAPH
A block-level paragraph. Described by the <p> element.

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 the <del> element. (Only if configured during parse.)

LOWDOWN_SUPERSCRIPT
A superscript. Described by the <sup> element. (Only if configured during parse.)

LOWDOWN_TABLE_BLOCK
A table block. Described by <table>. (Only if configured during parse.)

LOWDOWN_TABLE_BODY
A table body section. Described by <tbody>. Parent is always LOWDOWN_TABLE_BLOCK. (Only if
configured during parse.)

LOWDOWN_TABLE_CELL
A table cell. Described by <td> or <th> if in the header. Parent is always
LOWDOWN_TABLE_ROW. (Only if configured during parse.)

LOWDOWN_TABLE_HEADER
A table header section. Described by <thead>. Parent is always LOWDOWN_TABLE_BLOCK. (Only
if configured during parse.)

LOWDOWN_TABLE_ROW
A table row. Described by <tr>. Parent is always LOWDOWN_TABLE_HEADER or
LOWDOWN_TABLE_BODY. (Only if configured during parse.)

LOWDOWN_TRIPLE_EMPHASIS
Combination of LOWDOWN_EMPHASIS and LOWDOWN_DOUBLE_EMPHASIS.

The following anonymous union structures correspond to certain nodes. Note that all buffers may be zero-
length.

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 elements.

rndr_entity
For LOWDOWN_ENTITY, the entity text.

rndr_footnote_def
For LOWDOWN_FOOTNOTE_DEF, the footnote number num (starting at one). This matches a single
LOWDOWN_FOOTNOTE_DEF similarly numbered. The key is its original in-document reference key.

rndr_footnote_ref
For a LOWDOWN_FOOTNOTE_REF reference to a LOWDOWN_FOOTNOTE_DEF, the footnote number num
(starting at one). The def is the content parsed as children to the matching
LOWDOWN_FOOTNOTE_DEF. The key is its original in-document reference key.

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 (the top-level header).

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.

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 element, and/or
HLIST_FL_BLOCK for list item output as if containing block elements. 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 displaymode: if 1, in-line math; if 2, multi-line.

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.

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 element.

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 be bits of HTBL_FL_ALIGN_LEFT, HTBL_FL_ALIGN_RIGHT, or HTBL_FL_ALIGN_CENTER when masked
with HTBL_FL_ALIGNMASK; or HTBL_FL_HEADER. The number of columns in rndr_table,
rndr_table_header, and rndr_table_cell are the same.

AUTHORS

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

NAME

LIBRARY

SYNOPSIS

DESCRIPTION

SEE ALSO

AUTHORS