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Description
For ::first-letter https://drafts.csswg.org/css-pseudo-4/#application-in-css says
In CSS the first letter of a table-cell or inline-block cannot be the first letter of an ancestor element. [...] If an element is a list item (display: list-item), the ::first-letter applies to the first letter in the principal box after the marker.
But for ::first-line https://drafts.csswg.org/css-pseudo-4/#first-text-line only has the first part
The first line of a table-cell or inline-block cannot be the first formatted line of an ancestor element.
Should markers be excluded too? testcase
.inside {
list-style-position: inside;
}
li::first-line {
color: magenta;
}
li::first-letter {
color: blue;
}
<ol>
<li class="inside">inside</li>
<li>outside</li>
</ol>
Chromium always excludes markers, Firefox includes them when they have inside positioning.