Add "Name from Content" accname step for ::marker pseudo-element (#2419)

Co-authored-by: Rahim Abdi 
Co-authored-by: James Nurthen 

Author: 3 people

accname/index.html

@@ -665,8 +665,13 @@ Computation steps
                       <span id="step2F.ii">span><em>Name From Generated Content:em> Check for
                       <abbr title="Cascading Style Sheets">CSSabbr> generated textual content associated with the <code>current nodecode> and include it in the <code>accumulated textcode>. The
                       <abbr title="Cascading Style Sheets">CSSabbr> <a href="https://www.w3.org/TR/selectors-3/#gen-content"><code>::beforecode> and <code>::aftercode>a> pseudo elements
-                      [[!CSS2]] can provide textual content for [=element|elements=] that have a content model.
+                      [[!CSS2]] can provide textual content for [=element|elements=] that have a content model, in addition to the
+                      <a href="https://www.w3.org/TR/css-pseudo-4/#selectordef-marker"><code>::markercode>a> pseudo element.
                       <ol class="acc-ol">
+                        <li id="comp_name_from_content_pseudo_element_marker">
+                          For <code>::markercode> pseudo elements, <a class="termref">User agentsa> MUST append <abbr title="Cascading Style Sheets">CSSabbr> textual content, without a space, to
+                          the textual content of the <code>current nodecode> if the <code>current nodecode> supports <code>::markercode>.
+                        li>
                         <li id="comp_name_from_content_pseudo_element_before">
                           For <code>::beforecode> pseudo elements, <a class="termref">User agentsa> MUST prepend <abbr title="Cascading Style Sheets">CSSabbr> textual content, without a space,
                           to the textual content of the <code>current nodecode>.