kramdown

fast, pure-Ruby Markdown-superset converter

HTML Converter

Introduction

This converter converts a kramdown element tree into an HTML fragment and supports all available element types. Below is a list of additional features of the HTML converter as well as some additional information.

Automatic Generation of Header IDs

kramdown supports the automatic generation of header IDs if the option auto_ids is set to true (which is the default). This is done by converting the untransformed, i.e. plain, header text (or, if the option auto_id_stripping is set, only the text from real text elements) via the following steps:

Note that the option auto_id_stripping will be removed in version 2.0 because this will be the default behaviour!

Following are some examples of header texts and their respective generated IDs:

Sample header generated ID generated ID with auto_id_stripping
# This is a header this-is-a-header this-is-a-header
## 12. Another one 1 here another-one-1-here another-one-1-here
### Do ^& it now do–it-now do–it-now
# Hallo hallo hallo
# Hallo hallo-1 hallo-1
# 123456789 section section
# <i>test</i> itesti test

The automatic creation of header IDs is not part of standard Markdown. The rules on how header text is converted to an identifier are based on the rules specified by Pandoc.

Such generated IDs are only used if no ID has been set manually before.

Code Blocks

A code block is wrapped in both <pre> and <code> tags.

Showing Whitespace in a Code Block

It is sometimes useful to visualize whitespace within a code block. This can be achieved by adding the class show-whitespaces to a code block (using a block IAL).

Here is an example where the whitespaces are shown:

	leadingtab	andspace
trailingtabandspace	

When showing whitespace in a code block, all spaces are replaced with the entity &sdot; and additionally spaces and tabs in the code block are marked up using HTML span tags and the following CSS classes:

Automatic Syntax Highlighting

kramdown supports setting a code language for code blocks and code spans, see Language of Code Blocks. This language will be used for highlighting code blocks and spans.

The actual syntax highlighting is configurable via the option ‘syntax_highlighter’. The default value is ‘coderay’ which implies that the Coderay syntax highlighter is used.

Another syntax highlighter is Rouge which is Pygments compatible, i.e. it supports all of Pygments CSS themes.

Math Support

kramdown supports the use of various math engines. The default math engine is MathJax.

Alternative math engines are Ritex and itex2MML both of which output MathML.

Emphasis

kramdown uses the HTML element em to style light and the element strong to style strong emphasized text parts.

Footnotes

If a document contains footnotes, they are automatically placed at the end of the document.

By assigning the reference name “footnotes” to an ordered or unordered list, the list will be replaced with the footnotes, instead of placing the footnotes at the end of the document.

Automatic “Table of Contents” Generation

kramdown supports the automatic generation of the table of contents of all headers that have an ID set. Just assign the reference name “toc” to an ordered or unordered list by using an IAL and the list will be replaced with the actual table of contents, rendered as nested unordered lists if “toc” was applied to an unordered list or else as nested ordered lists. All attributes applied to the original list will also be applied to the generated TOC list and it will get an ID of markdown-toc if no ID was set.

When the auto_ids option is set, all headers will appear in the table of contents as they all will have an ID. Assign the class name “no_toc” to a header to exclude it from the table of contents.

Here is an example:

# Contents
{:.no_toc}

* Will be replaced with the ToC, excluding the "Contents" header
{:toc}

# H1 header

## H2 header

Options

The HTML converter supports the following options:

auto_ids
Use automatic header ID generation

If this option is true, ID values for all headers are automatically generated if no ID is explicitly specified.

Default: true
Used by: HTML/Latex converter

auto_id_prefix
Prefix used for automatically generated header IDs

This option can be used to set a prefix for the automatically generated header IDs so that there is no conflict when rendering multiple kramdown documents into one output file separately. The prefix should only contain characters that are valid in an ID!

Default: ‘’
Used by: HTML/Latex converter

auto_id_stripping
Strip all formatting from header text for automatic ID generation

If this option is true, only the text elements of a header are used for generating the ID later (in contrast to just using the raw header text line).

This option will be removed in version 2.0 because this will be the default then.

Default: false
Used by: kramdown parser

transliterated_header_ids
Transliterate the header text before generating the ID

Only ASCII characters are used in headers IDs. This is not good for languages with many non-ASCII characters. By enabling this option the header text is transliterated to ASCII as good as possible so that the resulting header ID is more useful.

The stringex library needs to be installed for this feature to work!

Default: false
Used by: HTML/Latex converter

template
The name of an ERB template file that should be used to wrap the output or the ERB template itself.

This is used to wrap the output in an environment so that the output can be used as a stand-alone document. For example, an HTML template would provide the needed header and body tags so that the whole output is a valid HTML file. If no template is specified, the output will be just the converted text.

When resolving the template file, the given template name is used first. If such a file is not found, the converter extension (the same as the converter name) is appended. If the file still cannot be found, the templates name is interpreted as a template name that is provided by kramdown (without the converter extension). If the file is still not found, the template name is checked if it starts with ‘string://’ and if it does, this prefix is removed and the rest is used as template content.

kramdown provides a default template named ‘document’ for each converter.

Default: ‘’
Used by: all converters

footnote_nr
The number of the first footnote

This option can be used to specify the number that is used for the first footnote.

Default: 1
Used by: HTML converter

entity_output
Defines how entities are output

The possible values are :as_input (entities are output in the same form as found in the input), :numeric (entities are output in numeric form), :symbolic (entities are output in symbolic form if possible) or :as_char (entities are output as characters if possible, only available on Ruby 1.9).

Default: :as_char
Used by: HTML converter, kramdown converter

smart_quotes
Defines the HTML entity names or code points for smart quote output

The entities identified by entity name or code point that should be used for, in order, a left single quote, a right single quote, a left double and a right double quote are specified by separating them with commas.

Default: lsquo,rsquo,ldquo,rdquo
Used by: HTML/Latex converter

toc_levels
Defines the levels that are used for the table of contents

The individual levels can be specified by separating them with commas (e.g. 1,2,3) or by using the range syntax (e.g. 1..3). Only the specified levels are used for the table of contents.

Default: 1..6
Used by: HTML/Latex converter

enable_coderay
Use coderay for syntax highlighting

If this option is true, coderay is used by the HTML converter for syntax highlighting the content of code spans and code blocks.

Default: true
Used by: HTML converter

coderay_wrap
Defines how the highlighted code should be wrapped

The possible values are :span, :div or nil.

Default: :div
Used by: HTML converter

coderay_line_numbers
Defines how and if line numbers should be shown

The possible values are :table, :inline or nil. If this option is nil, no line numbers are shown.

Default: :inline
Used by: HTML converter

coderay_line_number_start
The start value for the line numbers

Default: 1
Used by: HTML converter

coderay_tab_width
The tab width used in highlighted code
Used by: HTML converter
coderay_bold_every
Defines how often a line number should be made bold

Can either be an integer or false (to turn off bold line numbers completely).

Default: 10
Used by: HTML converter

coderay_css
Defines how the highlighted code gets styled

Possible values are :class (CSS classes are applied to the code elements, one must supply the needed CSS file) or :style (default CSS styles are directly applied to the code elements).

Default: style
Used by: HTML converter

coderay_default_lang
Sets the default language for highlighting code blocks

If no language is set for a code block, the default language is used instead. The value has to be one of the languages supported by coderay or nil if no default language should be used.

Default: nil
Used by: HTML converter

syntax_highlighter
Set the syntax highlighter

Specifies the syntax highlighter that should be used for highlighting code blocks and spans. If this option is set to +nil+, no syntax highlighting is done.

Options for the syntax highlighter can be set with the syntax_highlighter_opts configuration option.

Default: coderay
Used by: HTML/Latex converter

syntax_highlighter_opts
Set the syntax highlighter options

Specifies options for the syntax highlighter set via the syntax_highlighter configuration option.

The value needs to be a hash with key-value pairs that are understood by the used syntax highlighter.

Default: {}
Used by: HTML/Latex converter

math_engine
Set the math engine

Specifies the math engine that should be used for converting math blocks/spans. If this option is set to +nil+, no math engine is used and the math blocks/spans are output as is.

Options for the selected math engine can be set with the math_engine_opts configuration option.

Default: mathjax
Used by: HTML converter

math_engine_opts
Set the math engine options

Specifies options for the math engine set via the math_engine configuration option.

The value needs to be a hash with key-value pairs that are understood by the used math engine.

Default: {}
Used by: HTML converter

footnote_backlink
Defines the text that should be used for the footnote backlinks

The footnote backlink is just text, so any special HTML characters will be escaped.

If the footnote backlint text is an empty string, no footnote backlinks will be generated.

Default: ‘&8617;’
Used by: HTML converter