LESS syntax highlighting in Geany

You can use GNU's source-highlight, as shown here (path may differ, see below):

 export LESSOPEN="| /usr/bin/src-hilite-lesspipe.sh %s"
 export LESS=' -R '

As of Debian Stretch and Fedora 25, package names and script paths differ

• Debian:

  sudo apt install libsource-highlight-common source-highlight
  dpkg -L libsource-highlight-common | grep lesspipe
  # /usr/share/source-highlight/src-hilite-lesspipe.sh
  

• Fedora:

  sudo dnf install source-highlight
  rpm -ql source-highlight | grep lesspipe
  # /usr/bin/source-highlight/src-hilite-lesspipe.sh
  

PSPad allows you to define "User highlighters". Although not quite as flexible as a full specification, you can at least define all the keywords (up to 3 categories) and reserved words you want highlighted. For LESS, you can get/edit a list of keywords from the existing CSS highlighter in the [Keywords] section from "CSS.DEF" in the "Context" directory inside the PSPad program folder -- you may also expand this list if you simply want support for the CSS3 keywords in the regular CSS highlighter.

You should then assign this user highlighter to one of the "<not assigned>" spots in the Highlighter Settings, following which you can select colours for the reserved words and 3 keyword categories.

With these user highlighters, nested brackets work just fine.

Note: since these files are stored in subfolders of the PSPad program folder, usually in C:\Program Files, Windows Vista and Windows 7 won't let you edit them unless you run PSPad as Administrator. Be sure to do this when you change any settings.

So, in summary:

• Expand C:\Program Files\PSPad\Context\CSS.DEF for CSS3 properties
• Create a user highlighter (with keywords from the above file) to be able to have syntax highlighting for LESS