UDL (User Defined Language) is one of most important features in Notepad++.
In v6.2, much better UDL system (UDL2) is provided by Ivan Radic (aka Loreia). Not only many restrictions/limitations in UDL are removed, but also a lot of new features/enhancements are added in UDL2. In fact, you can almost define any language with it.
The key features of UDL2 are:
1. More keyword groups were added (more syntax highlighting can be defined):
3 folding groups
8 keyword groups
2 comment groups
1 number definitons
2 operators groups
8 delimiter sets
2. Multipart keywords are supported (for example: "else if" can be defined as a single keyword)
3. Whitespace is no longer mandatory as keyword separator: Operators, Delimiters and Folding keywords can be recognized with or without whitespace separators.
4. Numbers recognition support is greatly improved (prefix, suffix, range and extra symbols supported).
5. Operators and delimiters can be longer than one character.
6. The same characters can be used as comments AND operators.
7. Comments and delimiters support nesting (even within each other).
8. Improvments to Comments include:
Comment only start at the beginning of line
9. In the case of several comment pairs defined, comment open symbols match only with comment close symbols of the same order. (for example: /* C comment */, /+ D comment +/, but not /* mixed comment +/)
Thank Loreia for this new shining UDL engine, and thank Christian Cuvier for his multi-part keyword and number enhancement in UDL2.