I was looking at the changes in C23, and found this in Annex M of the C23 draft:

d (U+0040, COMMERCIAL AT), $ (U+0024, DOLLAR SIGN), and ` (U+0060, GRAVE ACCENT, “Backtick”) into the source and execution character set;

What is difference between “source character set” and “execution character set”? Are $, @, and ` allowed in identifiers in C23?