Mode Reference

Types

Types of attributes values in this reference:

identifier String suitable to be used as a JavaScript variable and CSS class name (i.e. mostly /[A-Za-z0-9_]+/)
regexp String representing a JavaScript regexp. Note that since it’s not a literal regexp all back-slashes should be repeated twice
boolean JavaScript boolean: true or false
number JavaScript number
object JavaScript object: { ... }
array JavaScript array: [ ... ]

Language Only Attributes

These attributes are only valid at the language level (ie, they many only exist on the top-most language object and have no meaning if specified in children modes).

name

  • type: string

The canonical name of this language, ie “JavaScript”, etc.

case_insensitive

  • type: boolean

Case insensitivity of language keywords and regexps. Used only on the top-level mode.

aliases

  • type: array

A list of additional names (besides the canonical one given by the filename) that can be used to identify a language in HTML classes and in a call to getLanguage.

classNameAliases

  • type: object

A mapping table of any custom class names your grammar uses and their supported equivalencies. Perhaps your language has a concept of “slots” that roughly correspond to variables in other languages. This allows you to write grammar code like:

{
  classNameAliases: {
    slot: "variable",
    "message-name": "string"
  },
  contains: [
    {
      className: "slot",
      begin: // ...
    }
  ]
}

The final HTML output will render slots with the CSS class as hljs-variable. This feature exists to make it easier for grammar maintainers to think in their own language when maintaining a grammar.

For a list of all supported class names please see the CSS class reference.

disableAutodetect

  • type: boolean

Disables autodetection for this language.

compilerExtensions (USE WITH CAUTION)

  • type: an array of compiler extensions ie: ``(mode, parentMode) -> {} ``

This allows grammars to extend the mode compiler to add their own syntactic sugar to make reading and writing grammars easier. Note: This is heavily dependent upon compiler internals and may NOT be stable from minor release to minor release. It is currently recommended only for 1st party grammars. The intention is that we use grammars to “test” out new compiler extensions and if they perform well promote them into the core library.

mode
The incoming mode object
parentMode
The parent mode of the mode (null for the top level language mode)

For example lets look at a tiny well behaved extension to allow us to write match as sugar to better express the intent to “match a single thing, then end mode”.

compilerExtensions: [
  (mode, _parentMode) => {
    // first some quick sanity checks
    if (!mode.match) return;

    // then check for users doing things that would make no sense
    if (mode.begin || mode.end) throw new Error("begin & end are not supported with match");

    // copy the match regex into begin
    mode.begin = mode.match;

    // cleanup: delete our syntactic construct
    delete mode.match;
  }
]

Compiler extension functions return nothing. They are expected to mutate the mode itself.

Mode Attributes

className

  • type: identifier

The name of the mode. It is used as a class name in HTML markup.

Multiple modes can have the same name. This is useful when a language has multiple variants of syntax for one thing like string in single or double quotes.

begin

  • type: regexp

Regular expression starting a mode. For example a single quote for strings or two forward slashes for C-style comments. If absent, begin defaults to a regexp that matches anything, so the mode starts immediately.

match

  • type: regexp

This is simply syntactic sugar for a begin when no end expression is necessary. It may not be used with begin or end keys (that would make no sense). It exists simply to help make grammars more readable.

{
  className: "title",
  match: /Fish/
}

on:begin

  • type: callback (matchData, response)

This callback is triggered the moment a begin match is detected. matchData includes the typical regex match data; the full match, match groups, etc. The response object is used to tell the parser how it should handle the match. It can be also used to temporarily store data.

  • response.data - a simple object data store. Can be used for building more complex rules where the end rule is dependent on the content of begin, etc.
  • response.ignoreMatch() - pretend as if this match never happened. The mode is not entered. Continues trying subsequent modes in the current mode’s contains list

For an example of usage see END_SAME_AS_BEGIN in modes.js.

end

  • type: regexp

Regular expression ending a mode. For example a single quote for strings or “$” (end of line) for one-line comments.

It’s often the case that a beginning regular expression defines the entire mode and doesn’t need any special ending. For example a number can be defined with begin: "\\b\\d+" which spans all the digits.

If absent, end defaults to a regexp that matches anything, so the mode ends immediately (after possibly matching any contains sub-modes).

Sometimes a mode can end not by itself but implicitly with its containing (parent) mode. This is achieved with endsWithParent attribute.

on:end

  • type: callback (matchData, response)

This callback is triggered the moment an end match is detected. matchData includes the typical regex match data; the full match, match groups, etc. The response object is used to tell the parser how it should handle the match. It can also be used to retrieve data stored from a begin callback.

  • response.data - a simple object data store. Can be used for building more complex rules where the end rule is dependent on the content of begin, etc.
  • response.ignoreMatch() - pretend as if this match never happened. The mode is not entered. Continues trying subsequent modes in the current mode’s contains list

For an example of usage see END_SAME_AS_BEGIN in modes.js.

beginKeywords

  • type: string

Used instead of begin for modes starting with keywords to avoid needless repetition:

{
  begin: '\\b(class|interface)\\b',
  keywords: 'class interface'
}

… can often be shortened to:

{
  beginKeywords: 'class interface'
}

Unlike the keywords attribute, this one allows only a simple list of space separated keywords. If you do need additional features of keywords or you just need more keywords for this mode you may include keywords along with beginKeywords.

Note: beginKeywords also checks for a . before or after the keywords and will fail to match if one is found. This is to avoid false positives for method calls or property accesses.

Ex. class A { ... } would match while A.class == B.class would not.

endsWithParent

  • type: boolean

A flag showing that a mode ends when its parent ends.

This is best demonstrated by example. In CSS syntax a selector has a set of rules contained within symbols “{” and “}”. Individual rules separated by “;” but the last one in a set can omit the terminating semicolon:

p {
  width: 100%; color: red
}

This is when endsWithParent comes into play:

{
  className: 'rules', begin: /\{/, end: /\}/,
  contains: [
    {className: 'rule', /* ... */ end: ';', endsWithParent: true}
  ]
}

endsParent

  • type: boolean

Forces closing of the parent mode right after the current mode is closed.

This is used for modes that don’t have an easily expressible ending lexeme but instead could be closed after the last interesting sub-mode is found.

Here’s an example with two ways of defining functions in Elixir, one using a keyword do and another using a comma:

def foo :clear, list do
  :ok
end

def foo, do: IO.puts "hello world"

Note that in the first case the parameter list after the function title may also include a comma. And if we’re only interested in highlighting a title we can tell it to end the function definition after itself:

{
  className: 'function',
  beginKeywords: 'def', end: /\B\b/,
  contains: [
    {
      className: 'title',
      begin: hljs.IDENT_RE, endsParent: true
    }
  ]
}

(The end: /\B\b/ regex tells function to never end by itself.)

endSameAsBegin (deprecated as of 10.1)

Deprecated: This attribute has been deprecated. You should instead use the END_SAME_AS_BEGIN mode or use the on:begin and on:end attributes to build more complex paired matchers.

  • type: boolean

Acts as end matching exactly the same string that was found by the corresponding begin regexp.

For example, in PostgreSQL string constants can use “dollar quotes”, consisting of a dollar sign, an optional tag of zero or more characters, and another dollar sign. String constant must be ended with the same construct using the same tag. It is possible to nest dollar-quoted string constants by choosing different tags at each nesting level:

$foo$
  ...
  $bar$ nested $bar$
  ...
$foo$

In this case you can’t simply specify the same regexp for begin and end (say, "\\$[a-z]\\$"), but you can use begin: "\\$[a-z]\\$" and endSameAsBegin: true.

lexemes (now keywords.$pattern)

  • type: regexp

A regular expression that extracts individual “words” from the code to compare against keywords. The default value is \w+ which works for many languages.

Note: It’s now recommmended that you use keywords.$pattern instead of lexemes, as this makes it easier to keep your keyword pattern associated with your keywords themselves, particularly if your keyword configuration is a constant that you repeat multiple times within different modes of your grammar.

keywords

  • type: object / string / array

Keyword definition comes in three forms:

  • 'for while if|0 else weird_voodoo|10 ... ' – a string of space-separated keywords with an optional relevance over a pipe
  • {keyword: ' ... ', literal: ' ... ', $pattern: /\w+/ } – an object that describes multiple sets of keywords and the pattern used to find them
  • ["for", "while", "if|0", ...] – an array of keywords (with optional relevance via |)

For detailed explanation see Language definition guide.

illegal

  • type: regexp or array

A regular expression or array that defines symbols illegal for the mode. When the parser finds a match for illegal expression it immediately drops parsing the whole language altogether.

{
  illegal: /%/,
  // or using an array
  illegal: [ /%/, /cookies/ ]
}

excludeBegin, excludeEnd

  • type: boolean

Exclude beginning or ending lexemes out of mode’s generated markup. For example in CSS syntax a rule ends with a semicolon. However visually it’s better not to color it as the rule contents. Having excludeEnd: true forces a <span> element for the rule to close before the semicolon.

returnBegin

  • type: boolean

Returns just found beginning lexeme back into parser. This is used when beginning of a sub-mode is a complex expression that should not only be found within a parent mode but also parsed according to the rules of a sub-mode.

Since the parser is effectively goes back it’s quite possible to create a infinite loop here so use with caution!

returnEnd

  • type: boolean

Returns just found ending lexeme back into parser. This is used for example to parse JavaScript embedded into HTML. A JavaScript block ends with the HTML closing tag </script> that cannot be parsed with JavaScript rules. So it is returned back into its parent HTML mode that knows what to do with it.

Since the parser is effectively goes back it’s quite possible to create a infinite loop here so use with caution!

contains

  • type: array

The list of sub-modes that can be found inside the mode. For detailed explanation see Language definition guide.

starts

  • type: identifier

The name of the mode that will start right after the current mode ends. The new mode won’t be contained within the current one.

Currently this attribute is used to highlight JavaScript and CSS contained within HTML. Tags <script> and <style> start sub-modes that use another language definition to parse their contents (see subLanguage).

variants

  • type: array

Modification to the main definitions of the mode, effectively expanding it into several similar modes each having all the attributes from the main definition augmented or overridden by the variants:

{
  className: 'string',
  contains: ['self', hljs.BACKSLASH_ESCAPE],
  relevance: 0,
  variants: [
    {begin: /"/, end: /"/},
    {begin: /'/, end: /'/, relevance: 1}
  ]
}

Note: variants has very specific behavior with regards to contains: ['self']. Lets consider the example above. While you might think this would allow you to embed any type of string (double or single quoted) within any other string, it does not allow for this.

The variants are compiled into to two discrete modes:

{ className: 'string', begin: /"/, contains: ['self', ... ] }
{ className: 'string', begin: /'/, contains: ['self', ... ] }

Each mode’s self refers only to the new expanded mode, not the original mode with variants (which no longer exists after compiling).

Further info: https://github.com/highlightjs/highlight.js/issues/826

subLanguage

  • type: string or array

Highlights the entire contents of the mode with another language.

When using this attribute there’s no point to define internal parsing rules like lexemes (now keywords.$pattern) or keywords. Also it is recommended to skip className attribute since the sublanguage will wrap the text in its own <span class="language-name">.

The value of the attribute controls which language or languages will be used for highlighting:

  • language name: explicit highlighting with the specified language
  • empty array: auto detection with all the languages available
  • array of language names: auto detection constrained to the specified set