Implement the new fields for plain list.

src/parser/plain_list.rs

@@ -153,6 +153,7 @@ where
     let mut children = Vec::new();
     let mut first_item_indentation: Option<IndentationLevel> = None;
     let mut first_item_list_type: Option<PlainListType> = None;
+    let contents_begin = remaining;
     let mut remaining = remaining;
 
     // The final list item does not consume trailing blank lines (which instead get consumed by the list). We have three options here:
@@ -196,7 +197,8 @@ where
         )));
     }
 
-    let (remaining, _trailing_ws) =
+    let contents = get_consumed(contents_begin, remaining);
+    let (remaining, post_blank) =
         maybe_consume_trailing_whitespace_if_not_exiting(context, remaining)?;
     let source = get_consumed(input, remaining);
     Ok((
@@ -209,6 +211,8 @@ where
             ),
             list_type: first_item_list_type.expect("Plain lists require at least one element."),
             children: children.into_iter().map(|(_start, item)| item).collect(),
+            contents: Some(Into::<&str>::into(contents)),
+            post_blank: post_blank.map(Into::<&str>::into),
         },
     ))
 }