The Syntax of PEG Markdown Highlight Stylesheets

PEG Markdown Highlight includes a parser for stylesheets that define how different Markdown language elements are to be highlighted. This document describes the syntax of these stylesheets.

Example

Here is a quick, simple example of a stylesheet:

Style Rules

A stylesheet is composed of one or more rules. Rules are separated from each other by empty lines like so:

H2:
foreground: ff0000

H3:
foreground: 00ff00

Each begins with the name of the rule, which is always on its own line, and may be one of the following:

• editor: Styles that apply to the whole document/editor
• editor-current-line: Styles that apply to the current line in the editor (i.e. the line where the caret is)
• editor-selection: Styles that apply to the selected range in the editor when the user makes a selection in the text
• A Markdown element type (like EMPH, REFERENCE or H1): Styles that apply to occurrences of that particular element. The supported element types are:
  • LINK: Explicit link (like [click here][ref])
  • AUTO_LINK_URL: Implicit URL link (like <http://google.com>)
  • AUTO_LINK_EMAIL: Implicit email link (like <first.last@google.com>)
  • IMAGE: Image definition
  • REFERENCE: Reference (like [id]: http://www.google.com)
  • CODE: Inline code
  • EMPH: Emphasized text
  • STRONG: Strong text
  • LIST_BULLET: Bullet for an unordered list item
  • LIST_ENUMERATOR: Enumerator for an ordered list item
  • H1: Header, level 1
  • H2: Header, level 2
  • H3: Header, level 3
  • H4: Header, level 4
  • H5: Header, level 5
  • H6: Header, level 6
  • BLOCKQUOTE: Blockquote marker
  • VERBATIM: Block of code
  • HRULE: Horizontal rule
  • HTML: HTML tag
  • HTML_ENTITY: HTML special entity definition (like …)
  • HTMLBLOCK: Block of HTML
  • COMMENT: (HTML) Comment
  • NOTE: Note
  • STRIKE: Strike-through

The name may be optionally followed by an assignment operator (either : or =):

H1:
foreground: ff00ff

H2 =
foreground: ff0000

H3
foreground: 00ff00

The order of style rules is significant; it defines the order in which different language elements should be highlighted. (Of course applications that use PEG Markdown Highlight and the style parser may disregard this and highlight elements in whatever order they desire.)

After the name of the rule, there can be one or more attributes.

Style Attributes

Attribute assignments are each on their own line, and they consist of the name of the attribute as well as the value assigned to it. An assignment operator (either : or =) separates the name from the value:

attribute-name: value
attribute-name= value

Attribute assignment lines may be indented.

Attribute Names and Types

The following is a list of the names of predefined attributes, and the values they may be assigned:

• foreground-color (aliases: foreground and color)
  • See the Color Attribute Values subsection for information about valid values for this attribute.
• background-color (alias: background)
  • See the Color Attribute Values subsection for information about valid values for this attribute.
• caret-color (alias: caret)
  • See the Color Attribute Values subsection for information about valid values for this attribute.
• strike-color (alias: strike)
  • See the Color Attribute Values subsection for information about valid values for this attribute.
• font-size
  • An integer value for the font size, in points (i.e. not in pixels). The number may have a textual suffix such as pt.
  • If the value begins with + or -, it is considered relative to some base font size (as defined by the host application). For example, the value 3 defines the font size as 3 (absolute) while +3 defines it as +3 (relative), i.e. 3 point sizes larger than the base font size.
• font-family
  • A comma-separated list of one or more arbitrary font family names. (It is up to the application that uses the PEG Markdown Highlight library to resolve this string to actual fonts on the system.)
• font-style
  • A comma-separated list of one or more of the following:
    • italic
    • bold
    • underlined

Applications may also include support for any custom attribute names and values they desire — attributes other than the ones listed above will be included in the style parser results, with their values stored as strings.

Color Attribute Values

Colors can be specified either in RGB (red, green, blue) or ARGB (alpha, red, green, blue) formats. In both, each component is a two-character hexadecimal value (from 00 to FF):

foreground: ff00ee  # red = ff, green = 00, blue = ee (and implicitly, alpha = ff)
background: 99ff00ee  # alpha = 99, red = ff, green = 00, blue = ee

Comments

Each line in a stylesheet may have a comment. The # character begins a line comment that continues until the end of the line:

# this line has only this comment
H1:  # this line has a style rule name and then a comment
foreground: ff0000  # this line has an attribute and then a comment