Johannes Odland wrote in https://lists.w3.org/Archives/Public/www-style/2017Nov/0024.html :

Hi

According to Selectors Level 3 the ::first-letter includes punctuation that precedes the first character. The example specifically shows a dropped cap with an opening quotation mark.

Although there are no hard and fast rules for initial caps, it is a common typographical practice to style the punctuation different than the letter itself. The punctuation can hang in the margin, and be styled in the same font and font-size as the body text so that the initial letter is flush with other initial letters that does not have punctuation.

In Norwegian typography it is considered bad practice not to leave the letter itself flush with the other letters.

http://theworldsgreatestbook.com/book-design-part-6/
http://www.typografi.org/dropcaps/initialer.html
http://www.typografi.org/dropcaps/assets/lite-sitattegn_714.jpg

As the spec is now it is hard to achieve good drop caps.

Should there be a way to select the initial-punctuation also?