This is available since release 2013-12-08 “Binky”.

LESS is a dynamic stylesheet language that compiles to CSS. It offers new mechanisms like variables, nesting, mixins, operators and functions when writing stylesheets.

DokuWiki's CSS dispatcher includes a PHP based LESS parser which means you can use the full advantage of this dynamic CSS preprocessing in your template and plugin styles. Of course this is completely optional you can also write plain old CSS.

LESS statements are parsed in .css and in .less files.

Please refer to the official lesscss.org documentation to learn about the language itself. We're using lessphp as a parser so any restrictions of that library apply (eg. you can't use JavaScript expressions).

When using LESS please keep the following things in mind:

• Use nesting sparsely. Nesting deeper that 3 or 4 levels usually isn't needed and does not improve readability and might even affect selector performance
• Prefix your mixins and variables. When you define your own mixins and variables try to avoid common names that might clash with other templates or plugins. Just as you would with your classes and IDs.

style.ini placeholders are available in your styles as LESS variables, prefixed with @ini_ and with the __ removed.

Eg. the __background__ placeholder becomes @ini_background in your LESS styles.

At the moment (current date: 2018-03-08) the newest version of lessphp is 0.4.0, which is included in DokuWiki 2017-02-19e “Frusterick Manners”. Please be aware the publication date of version 0.4.0 is August 09 2013! (Changelog) That means some features of the current less.js (which is the primary less-compiler) are not supported by this version.

Nevertheless you can achieve advanced technics, but less convenient. As shown in the following realization of an “IF-Statement”, which is capable to include or exclude several CSS-rules at one blow.

On page leafo.net/lessphp there is an online compiler which gives the possibility to rapid testing what code snippet works and what doesn't.

This LESS-code:

@my-option: false;

.my-optional-style() when (@my-option = false) {
    #main_body { background-color: red; }
    p { color: green; }
}

.my-optional-style() when (@my-option = true) {
    #main_body { background-color: green; }
    p { color: black; }
}

.my-optional-style();

compiles to this CSS-code:

#main_body {
  background-color: red;
}
p {
  color: green;
}

Because all CSS has to pass through the LESS parser, we're a bit more strict on valid CSS. If your plugin uses invalid CSS it will likely throw an error now. A list of currently known problems is available at Less CSS Errors.