The Front Matter

Capture everything between the opening and closing --- markers of a Markdown front-matter block.

The dot matches any character except a line terminator. That single exception is why "just use .*" stops working the moment your input has more than one line. The s flag — dotAll — removes the exception. The long-hand alternative is a character class that covers everything, [\s\S], which costs four characters more than the flag does. Two things then bite. The block is the one at the START of the file, so anchor it — otherwise a --- further down can open a block of its own. And it ends at the FIRST closing marker: a Markdown horizontal rule in the body is three dashes too, and a greedy .* will happily swallow the whole document to reach it.