Bluefish Editor

Bluefish is a powerful editor targeted towards programmers and web developers, with many options to write websites, scripts and programming code. Bluefish supports a wide variety of programming and markup languages and has many features, e.g.

- Customizable code folding, auto indenting and completion - Support for remote files operation over FTP, SFTP, HTTPS, WebDAV, etc. - Site upload and download - Powerful search and replace engine - Customizable integration of external programs such as lint, make, etc - Snippets plugin to automate often used code - Code-aware in-line spell checking - Zencoding or Emmet support - Bookmarks panel

but is still lightweight and fast.

For validation of CSS/HTML/XML documents you need csstidy, tidy, weblint and/or xmllint. For preview to work, you need a web browser that can view local files given to it on the command line. For PHP or Python bluefish supports php-codesniffer and pylint. Tools not suggested but supported are make, perl, php5-cli and java-compiler.