Add support for reading & writing <mark> elements

Parse <mark> elements from HTML as HTML span like elements, with a
single class matching the tag name `mark`. Mark elements are rendered to
HTML using the native <mark> element.

Fixes https://github.com/jgm/pandoc/issues/5797.

src/Text/Pandoc/Shared.hs

@@ -698,7 +698,7 @@ underlineSpan = B.spanWith ("", ["underline"], [])
 -- | Set of HTML elements that are represented as Span with a class equal as
 -- the element tag itself.
 htmlSpanLikeElements :: Set.Set T.Text
-htmlSpanLikeElements = Set.fromList [T.pack "kbd"]
+htmlSpanLikeElements = Set.fromList [T.pack "kbd", T.pack "mark"]
 
 -- | Returns the first sentence in a list of inlines, and the rest.
 breakSentence :: [Inline] -> ([Inline], [Inline])

test/command/5797.md

@@ -0,0 +1,20 @@
+```
+% pandoc -f html -t html
+<mark>Ctrl-C</mark>
+^D
+<mark>Ctrl-C</mark>
+```
+
+```
+% pandoc -f html -t native
+<mark>Ctrl-C</mark>
+^D
+[Plain [Span ("",["mark"],[]) [Str "Ctrl-C"]]]
+```
+
+```
+% pandoc -f native -t html
+[Plain [Span ("",["mark"],[]) [Str "Ctrl-C"]]]
+^D
+<mark>Ctrl-C</mark>
+```