No, any program that can read text. Markdown is irrelevant for this.
I can do this offline and on mobiles.
No. They’re just a text string. But a curated or semi-curated text string which adds extra power to a whole text search.
That’s the point. It’s a choice. Some people like folders. Some people don’t. Some people are very good at advanced regex type searches, others aren’t. Some files fit comfortably into one box, others don’t.