Highlight markdown+mustache syntax for mardown mustache files.
This package adds a new grammar named
source.gfm.mustache, used by default for files with extension
You should add such grammar in the settings of other installed Atom packages related to markdown text editing (eg. in spell-check settings, in order to enable spell check also for markdown mustache files; in markdown-enhanced-preview, in order to enable preview of markdown mustache files; etc.)
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.