First take at flymake-csslint.el.

Very much based on flymake-jshint.

Author: arnested

README.md

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+# flymake-csslint.el
+
+To use CSSLint with emacs, you will need CSSLint installed and available on
+your path. You should be able to do
+
+	$ csslint
+
+without problem. To do this, you can install node.js, npm and
+csslint by doing the following:
+
+	$ apt-get install nodejs # or your distro / OS equivalent
+	$ curl http://npmjs.org/install.sh | sh
+	$ npm install -g csslint
+
+flymake-csslint.el is very much based on flymake-jshint.el by
+[Wilfred Hughes](<me@wilfred.me.uk>).
+
+## Usage
+
+Add to your emacs config:
+
+	(require 'flymake-csslint)
+	(add-hook 'css-mode-hook 'flymake-mode)
+
+making sure that flymake-csslint.el is on your load-path. If not,
+also add to your config:
+
+	(add-to-list 'load-path "~/.emacs.d/path/to/flymake-csslint.el")
+
+## Debugging
+
+If CSSLint isn't working for any reason, execute
+
+	M-x set-variable flymake-log-level <RET> 3
+
+and you will see what is going wrong listed in the *Messages*
+buffer.

flymake-csslint.el

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+;;; flymake-csslint.el --- making flymake work with CSSLint
+
+;; Copyright (C) 2011 Wilfred Hughes <me@wilfred.me.uk>
+;; Copyright (C) 2011 Arne J,Ax(Brgensen <arne@arnested.dk>
+
+;; Author: Arne J,Ax(Brgensen <arne@arnested.dk>
+;; Created: 1 December 2011
+;; Version: 1.0
+;; Keywords: flymake, csslint, css
+
+;; This file is not part of GNU Emacs.
+;; However, it is distributed under the same license.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 3, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+;; Boston, MA 02110-1301, USA.
+
+;;; Commentary
+
+;; To use CSSLint with emacs, you will need CSSLint installed and available on
+;; your path. You should be able to do
+
+;; $ csslint
+
+;; without problem. To do this, you can install node.js, npm and
+;; csslint by doing the following:
+
+;; $ apt-get install nodejs # or your distro / OS equivalent
+;; $ curl http://npmjs.org/install.sh | sh
+;; $ npm install -g csslint
+
+;; flymake-csslint.el is very much based on flymake-jshint.el by
+;; Wilfred Hughes <me@wilfred.me.uk>.
+
+;;; Usage
+
+;; Add to your emacs config:
+
+;; (require 'flymake-csslint)
+;; (add-hook 'css-mode-hook 'flymake-mode)
+
+;; making sure that flymake-csslint.el is on your load-path. If not,
+;; also add to your config:
+
+;; (add-to-list 'load-path "~/.emacs.d/path/to/flymake-csslint.el")
+
+;;; Debugging
+
+;; If CSSLint isn't working for any reason, execute
+
+;; M-x set-variable flymake-log-level <RET> 3
+
+;; and you will see what is going wrong listed in the *Messages*
+;; buffer.
+
+(require 'flymake)
+
+(defun flymake-csslint-init ()
+  (let* ((temp-file (flymake-init-create-temp-buffer-copy
+		     'flymake-create-temp-inplace))
+         (local-file (file-relative-name
+		      temp-file
+		      (file-name-directory buffer-file-name))))
+    (list "csslint" (list "--format=compact" local-file))))
+
+(setq flymake-allowed-file-name-masks
+      (cons '(".+\\.css$"
+	      flymake-csslint-init
+	      flymake-simple-cleanup
+	      flymake-get-real-file-name)
+	    flymake-allowed-file-name-masks))
+
+(setq flymake-err-line-patterns
+      (cons '("^\\(.*\\): line \\([[:digit:]]+\\), col \\([[:digit:]]+\\), \\(.+\\)$"
+	      1 2 3 4)
+	    flymake-err-line-patterns))
+
+; load flymake automatically in CSS mode
+(add-hook 'css-mode-hook 'flymake-mode)
+
+(provide 'flymake-csslint)
+
+;;; flymake-csslint.el ends herep