Last modified on 3 May 2015, at 06:56

User:Remember the dot/Syntax highlighter

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Dot's Syntax Highlighter 2012-12-06.png

I've created a script that makes syntax stand out colorfully in the edit box. Unlike other syntax highlighter scripts such as wikEd, AceWikiEditor, and CodeMirror, this one:

  • Updates the highlighting automatically as you type.
  • Does not break the Undo and Redo buttons.
  • Does not break spellcheck.
  • Is compatible with most other scripts that affect the edit box.


Please be sure to read the "Known issues" section below before installing the script.

For end user if installed on wikiEdit

If the syntax highlighter is available as a gadget on your wiki, go to your preferences and enable it.

For end user if not installed on wikiEdit

If installation as a gadget is not available, add these lines to your common.js page:

//syntax highlighter

For example, if the English Wikipedia did not provide the syntax highlighter as a gadget, you would add it to

For administrators of Wikimedia sitesEdit

On your wiki create the page MediaWiki:Gadget-DotsSyntaxHighlighter.js‎ with the code


Then add to the page MediaWiki:Gadgets-definition‎ a new line


and create the page MediaWiki:Gadget-DotsSyntaxHighlighter‎ with the text

[[mw:User:Remember the dot/Syntax highlighter|Syntax highlighter]]: Make syntax stand out colourfully in the edit box.

For administrators of non-Wikimedia sitesEdit

On your wiki create the page MediaWiki:Gadget-DotsSyntaxHighlighter.js‎ and copy the source code from User:Remember the dot/Syntax highlighter.js into it. Then add to the page MediaWiki:Gadgets-definition‎ a new line


and create the page MediaWiki:Gadget-DotsSyntaxHighlighter‎ with the text

[ Syntax highlighter]: Make syntax stand out colourfully in the edit box.

MediaWiki 1.22 or later is required.

Known issuesEdit


  1. The highlighter works best in the latest version of Firefox.
  2. The highlighter works almost all of the time in the latest versions of Chrome, Safari, and Opera, but does not work right with text written in certain scripts, notably Thai and Tibetan.
  3. The highlighter does not work in Internet Explorer (its bugs are too severe). The highlighter does not even attempt to execute if Internet Explorer is detected.
  4. The highlighter is not compatible with certain scripts that affect the edit box.


  1. For performance reasons, the highlighter requires all tags to be valid XML. For example, make sure that if you start a <p> tag you end it with </p>, and use <br/> instead of <br>.
  2. For performance reasons, the syntax highlighter can't handle '''apostrophe italic'' or ''italic apostrophe'''—it considers them invalid syntax. I suggest using '<i>apostrophe italic</i> and <i>italic apostrophe'</i> instead.
  3. <pre> tags created by putting a space at the beginning of a line are not highlighted. This is because the highlighter is not smart enough to tell when a space at the beginning of a line is simply whitespace inside a template.
  4. Behavior switches such as __NOTOC__ are not highlighted.
  5. External links created with {{fullurl:}} or templates are not highlighted. You will see [{{fullurl:My page}} external link] instead of [{{fullurl:My page}} external link].


  1. The highlighter does not perform well when editing long articles and will automatically disable itself if it delays more than 50ms. If this happens, a message appears explaining what happened and suggesting how to work around it or increase the timeout.
  2. The highlighter does not execute when uploading files.
  3. The highlighter may override your user styles related to the editing textbox.



It's easy to change the highlighter to use different colors or to not highlight certain syntaxes. The following color customizations are available:

defaultColor for recognized syntax elements that don't have a specific color defined
boldOrItalicColor '''bold''' ''italic''
wikilinkColor [[wikilink]]
externalLinkColor [http:// named external link], [],
headingColor ==Heading==, ;Small heading
listOrIndentColor * unordered list, # ordered list, : indent
signatureColor ~~~~
tableColor {| table |}
templateColor {{template}}
parameterColor {{{template parameter}}}
hrColor ----
tagColor <tag>...</tag>, <tag/>
commentColor <!-- comment -->
entityColor &entity;

For example, to make wikilinks cyan and external links orange, put the following in your common.js (if you installed the highlighter as a gadget, omit the first two lines):

//syntax highlighter
syntaxHighlighterConfig = {
    externalLinkColor: "#FFCC66", //orange
    wikilinkColor: "#E6FFFF", //cyan

To not highlight a syntax, set its color to "". For example, to disable external link highlighting:

//syntax highlighter
syntaxHighlighterConfig = {
    externalLinkColor: "",

To not highlight any syntax except those you explicitly want, set defaultColor to "" and set the color of each syntax you want to highlight. If you just want the usual color, set the color to "normal". For example, to only highlight tags:

//syntax highlighter
syntaxHighlighterConfig = {
    defaultColor: "",
    tagColor: "normal",


You can specify a timeout that replaces the default 50ms timeout. For example, if you're OK with sluggishness as you type and you want to disable highlighting only if it takes more than 75ms, put the following in your common.js:

//syntax highlighter
syntaxHighlighterConfig = {
    timeout: 75,

Again, if you installed the highlighter as a gadget, omit the first two lines.

Reporting bugsEdit

Note: Remember to check whether the bug you want to report is already a known issue.

When reporting bugs to me, please include:

Source codeEdit

To reduce download time and because the ResourceLoader does not automatically minify scripts imported from other wikis, MediaWiki:Gadget-DotsSyntaxHighlighter.js itself is kept in minified form. The actual source code is available at User:Remember the dot/Syntax highlighter.js.

Overview of approachEdit

This script creates a background div, named wpTextbox0, that is inserted behind wpTextbox1, the editing textbox. wpTextbox0 and wpTextbox1 are synchronized in style, and the background of wpTextbox1 is made transparent so that wpTextbox0 shows through. Then, blocks of text are added to wpTextbox0 as span elements. The text on the blocks is transparent, but the backgrounds of the blocks are colored. By using the same text in wpTextbox0 as wpTextbox1, any positioning anomalies from dynamically composed characters are eliminated. Because wpTextbox0 and wpTextbox1 are (theoretically) perfectly synchronized, the colored backgrounds appear to the user as though they have been added directly to wpTextbox1.

The text in wpTextbox0 is not actually added to the textContents of the span elements. Instead, it is added to the :before and :after pseudo-elements of each span using a dynamically generated CSS stylesheet. This avoids problems when trying to use the browser's find-in-page feature, because if textContent were used instead of CSS content, the browser would perceive both the real text in wpTextbox1 and the transparent text in wpTextbox0 to be on the page.