Notepad++ Custom Language Highlighting

There's a useful help page that explains how to use the GUI to define a custom language for Notepad++. As Alex K noted in a comment above, the option for setting string delimiters appears to be in the Delimiters boxes in the Operators tab. It doesn't look like it supports different colours for different levels of nesting, though.

I had log4net files that I wanted to view in Notepad++. They contained lines like:

2015-06-03 16:38:10,751 [Compname][Thread:29][FATAL]

To highlight [FATAL] just the keyword list wasn't enough. I added this: On tabpage "Folder & Default" > Folding in code style 1: >

Open: [ 
Close: ]

On tabpage "Keyword lists" > 1ste group > FATAL with some styling.

Update for those who have been asking the same question:

(Temporary) Documentation for custom syntax highlighting is on: http://udl20.weebly.com/index.html

There is a link to this in Notepad++ but it doesn't stand out.