Version 0.4 of package Rnc-Mode has just been released in GNU ELPA. You can now find it in M-x list-packages RET.
Rnc-Mode describes itself as: ========================================= Emacs mode to edit Relax-NG Compact files ========================================= More at https://elpa.gnu.org/packages/rnc-mode.html ## Summary: Provides mostly indentation, syntax highlighting, and Imenu support. Partly based on the info in https://relaxng.org/compact-20021121.html. ## Recent NEWS: Since 0.3: - Understands '...' strings.
