The |compacte filter is applied to a CSS or JavaScript file[The file to which the filter is applied must have either ".js" or ".css" as its filename extension.]] and creates a compressed copy which is smaller than the original as it deletes all comments, empty declarations, unnecessary blank spaces and lines etc. [1] (for Javascript files, the filter uses the JavaScriptPacker class).
Ater having archived this new file into the local/ directory, the filter returns the link: [<link rel="stylesheet" href="(#CHEMIN{spip_style.css}|compacte)" type="text/css" media="all" />] which will return something like: <link rel="stylesheet" href="local/cache-css/spip_style-compacte-092e.css" type="text/css" media="all" />