"Wait, why should I use this?" Good question! Lets ask the official SetlX-Tutorial:
I'm fairly sure you are convinced now ;)
This extension includes a syntax highlighter and a library of snippets to ease the development of SetlX-programs.
For more information, please visit the GitHub-Repository, where you obviously can also find the source code and can contribute to it. The SemVer-Number of this Extension is always kept in sync with the SublimeText-Extension living in the master-branch there.