This is a TextMate/Sublime/VS Code/Atom bundle providing language support for x86_64 assembly language in a variety of dialects (nasm/yasm primarily, but could highlight tasm/gas to some extent).
Atom package is exported from Textmate/Sublime Bundle, all issues and pull requests should be filed there.
To compile the yaml sources to tmLanguage, you'll need PackageDev.
YASM tests are provided by yasm-regression project.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.